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<!DOCTYPE html>
<html lang="en">
<head>
<!-- Global site tag (gtag.js) - Google Analytics -->
<script async src="https://www.googletagmanager.com/gtag/js?id=UA-10896062-3"></script>
<script>
window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());
gtag('config', 'UA-10896062-3');
</script>
<title>Healthy Living</title>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, height=device-height, initial-scale=1.0">
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.3/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.bundle.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/lazyload@2.0.0-rc.2/lazyload.js"></script>
<script src="js/background.js"></script>
<link rel="stylesheet" href="css/accordion.css" />
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" />
<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.8.2/css/all.css">
<link rel="stylesheet" href="https://use.typekit.net/hgq1zqp.css" />
<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Montserrat:300%7CPlayfair+Display&display=swap" />
<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Source+Sans+Pro:200,300,400,600,700&display=swap">
<link rel="stylesheet" href="css/background.css" />
<link rel="stylesheet" href="css/nav.css" />
</head>
<body>
<!-- Help Menu -->
<div class="modal fade" id="helpModal">
<div class="modal-dialog modal-xl">
<div class="modal-content help-menu-content">
<div class="container-fluid m-0 p-0">
<div class="row h-100 mh-100">
<div class="col-md-3">
<ul class="help-menu-list">
<li data-value="intro" class="help-menu-list-item active"><h4 class="help-menu-list-title">Introduction</h4></li>
<li data-value="accordion" class="help-menu-list-item"><h4 class="help-menu-list-title">Accordion Menu</h4></li>
<li data-value="content" class="help-menu-list-item"><h4 class="help-menu-list-title">Content</h4></li>
</ul>
</div>
<div class="col-md-9">
<div class="help-section" id="help-intro">
<div class="modal-header">
<h4 class="modal-title">Introduction to the Background Help Menu</h4>
<button type="button" class="close" data-dismiss="modal">×</button>
</div>
<div class="modal-body help-body">
<p class="help-menu-p">
The <b>help menu</b> exists to provide you with information about how to <b>use this website most effectively</b>. This specific help menu is targeted at the <b>background</b> portion of the healthy living website. If you need help regarding the application portion of the living website, or simply want to learn more about the fundamentals of circadian lighting, click <a href="application.html"> here </a> to navigate to the application page. Click "help" in the top navigation bar again to access the application page's respective help menu.
</p>
<p class="help-menu-p">
To begin your research via the Healthy Patterns website, simply click the "Background" button, or scroll down past the landing section.
</p>
<figure class="w-95 text-center mobile-figure"><img data-src="img/help/background/intro/1.png" class="lazy-load enlarge w-85 my-4 rounded drop-shadow" ></figure>
</div>
</div>
<div class="help-section d-none" id="help-accordion">
<div class="modal-header">
<h4 class="modal-title">Accordion Menu</h4>
<button type="button" class="close" data-dismiss="modal">×</button>
</div>
<div class="modal-body help-body">
<p class="help-menu-p">
Upon clicking the "Background" button on the Healthy Living landing page, your browser will be <b>automatically scrolled</b> down to a page that looks like this, with the <b>left most section</b> being the <b>accordion menu.</b>
</p>
<figure class="w-95 text-center mobile-figure"><img data-src="img/help/background/accordion/1.png" class="lazy-load enlarge w-85 my-4 rounded drop-shadow" ></figure>
<p>
The <b>accordion menu</b> is a type of <b>navigation menu</b> that allows you to find the information you are looking for very quickly. The accordion menu has a maximum of <b>three levels</b>, which can be seen in the figure below.
</p>
<figure class="w-95 text-center mobile-figure"><img data-src="img/help/background/accordion/2.png" class="lazy-load enlarge w-50 my-4 rounded drop-shadow" ></figure>
<p>
The First level category, <i>Healthcare</i>, has the second level categories: <i>General Information</i>, <i>Occupants</i>, <i>Specialty Information</i>, and <i>Summary</i> beneath it. It is clear which of these second level categories have third level categories underneath them due to the icons next to them. Second level accordion menu categories <b>with</b> icons next to them <b>have</b> third level categories below them. Second level accordion menu categories <b>without</b> icons next to them <b>do not have</b> third level categories below them. In the figure above we have <i>Healthcare > Speicalty Information > Lighting in the NICU</i> selected.
</p>
<p>
Use the accodion menu to navigate the content of the background page quickly.
</p>
</div>
</div>
<div class="help-section d-none" id="help-content">
<div class="modal-header">
<h4 class="modal-title">Content</h4>
<button type="button" class="close" data-dismiss="modal">×</button>
</div>
<div class="modal-body help-body">
<p>
The <b>content</b> portion of the background page is where the user can gather the information necessary to understand the work the LRC, and the <b>Light and Health Institute</b> in particular, is working on. The content can be navigated via the accordion menu on the left side. To learn more about how to use the accordion menu, click the "Accordion Menu" tab to the left of the help menu.
</p>
<figure class="w-95 text-center mobile-figure"><img data-src="img/help/background/content/3.png" class="lazy-load enlarge w-85 my-4 rounded drop-shadow" ></figure>
<h3 class="help-menu-header">Downloads</h3>
<p>
There exists a <b>Downloads</b> section under <b>Additional Information</b> in the accordion menu where you can find all the downloads mentioned throughout the background text. These downloadable PDF's provide a <b>summary</b> of their respective content.
</p>
<figure class="w-95 text-center mobile-figure"><img data-src="img/help/background/content/4.png" class="lazy-load enlarge w-85 my-4 rounded drop-shadow" ></figure>
<h3 class="help-menu-header">Glossary</h3>
<p>
There exists a <b>Glossary</b> section under <b>Additional Information</b> in the accordion menu where you can find vocabulary words used throughout the background text and their <b>definitions</b>.
</p>
<figure class="w-95 text-center mobile-figure"><img data-src="img/help/background/content/5.png" class="lazy-load w-85 my-4 rounded drop-shadow" ></figure>
<h3 class="help-menu-header">References</h3>
<p>
There exists a <b>References</b> section under <b>Additional Information</b> in the accordion menu where you can find all of the <b>cited sources</b> the background text references. These sources are also cited in-line in the background text.
</p>
<figure class="w-95 text-center mobile-figure m-0"><img data-src="img/help/background/content/6.png" class="lazy-load enlarge w-25 my-4 rounded drop-shadow" ></figure>
<p>
If you <b>hover</b> over one of these citations, its reference will pop up in a bubble above the citation. If you <b>click</b> on the reference, you will be brought to that reference in the <b>References</b> section.
</p>
<figure class="w-95 text-center mobile-figure"><img data-src="img/help/background/content/7.png" class="lazy-load w-85 my-4 rounded drop-shadow" ></figure>
<h3 class="help-menu-header">Suggestions/Report a Bug</h3>
<p>
If at any point when using the <b>Healthy Living</b> website you come across something that doesn't seem to be functioning as intended, we would greatly appreciate if you submit report it to us via the <b>Suggestions/Report a Bug</b> section under <b>Additional Information</b>. There you can fill out a <b>google form</b> and describe what went wrong.
</p>
<figure class="w-95 text-center mobile-figure"><img data-src="img/help/background/content/8.png" class="lazy-load enlarge w-85 my-4 rounded drop-shadow" ></figure>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<!-- Image Enlarge Modal -->
<div class="modal fade" id="enlarge_modal">
<div class="modal-dialog modal-xxl bg-transparent no-border">
<div class="modal-content bg-transparent no-border">
<div class="modal-bodyw-100 text-center" id="img_enlarge">
</div>
</div>
</div>
</div>
<!-- Navbar -->
<div id="navbar" class="position-fixed bb">
<script>
$('#navbar').load('navbar.html',function(){
$('#background-tab').addClass('active');
$('#application-tab').attr("href", "application.html");
});
</script>
</div>
<!-- Banner -->
<div class="container-fluid h-100vh overflow-hidden">
<div class="row banner">
<div class="col">
<div class="banner-text text-center">
<div class="middle">
<h1 class="banner-title d-none d-md-block">Lighting for Healthy Living</h1>
<h1 class="banner-title d-block d-md-none">Lighting<br />for<br />Healthy<br />Living</h1>
<p class="box-text mb-4 d-none d-md-block">This website integrates
recent developments in lighting research and education, bridging
them to lighting applications in real-world situations by providing
design suggestions that meet the unique needs of the people who occupy
specific places.<br /><span class=" d-md-block"><br />To learn more
about lighting and its impact on the circadian system, visit the <b>Background</b> page.</span><span class=" d-md-block"><br />To learn more
about how to apply circadian-effective design, visit the <b>Application</b> page.</span></p>
<button id="backgroundButton" class="btn btn-lg btn-primary mr-5">Background</button>
<a class="btn btn-lg btn-primary" href="application.html">Application</a>
</div>
</div>
<footer class="footer">
<p class="footer-p">© <script>document.write(new Date().getFullYear())</script> Lighting Research Center All Rights Reserved</p>
</footer>
</div>
</div>
</div>
<!-- bTT -->
<a id="backToTop"><i class="fas fa-angle-up fa-3x"></i></a>
<!-- Everything Below Banner -->
<div id="contentRow-container" class="container-fluid h-100-offset mh-100-offset overflow-hidden">
<div id="contentRow" class="row h-100-offset mh-100-offset">
<!-- Accordion -->
<div class="col-xl-3 col-lg-4 col-md-5 col-sm-12 p-0 accordion h-100-offset">
<div class="jquery-accordion-menu">
<nav class="acnav">
<a class="d-block d-md-none accordion-title-a" data-toggle="collapse" href="#accordionCollapse" role="button" aria-expanded="true" aria-controls="accordionCollapse">
<div>
<h4 class="accordion-title">Navigate</h4>
</div>
</a>
<div id="accordionCollapse" class="collapse show">
<ul class="acnav__list acnav__list--level1">
<li id="fundamentals" class="acLevel1 has-children">
<div class="acnav__label fundamentalsIcon">
<a>Fundamentals</a>
</div>
<!-- start level 2 -->
<ul class="acnav__list acnav__list--level2">
<li>
<a id="accordion-ourRole" class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-ourRole">Our Role</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-whatIsLight">What is Light?</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-lightingAndtheCircadianSystem">Light and the Circadian System</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-theSleepWakeCycle">The Sleep/Wake Cycle</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-theEye">The Eye</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-theRetina">The Retina</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-rodsAndCones">Rods and Cones</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-nonVisualSystems">Non-visual Systems</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-whatIsCircadianLighting">What is Circadian Lighting?</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-fundamentalsSummary">Summary</a>
</li>
</ul>
<!-- end level 2 -->
</li>
<li id="manufacturers" class="acLevel1 has-children">
<div class="acnav__label manufacturersIcon">Manufacturers / Designers</div>
<ul class="acnav__list acnav__list--level2">
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-componentsOfCircadianDesign">Components of Circadian Design</a>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-informationAboutRoom"><div class="acnav__label acnav__label--level2 manufacturersInnerIcon">Information about Room</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-facilityAndRoomType">Facility and Room Type</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-occupantType">Occupant Type</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-areaOfRoom">Area of Room</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-ceilingHeight">Ceiling Height</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-roomReflectances">Room Reflectances</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-furnitureLayout">Furniture Layout</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-horizontalIlluminance">Horizontal Illuminance</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-verticalIlluminance">Vertical Illuminance</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-evehratio">E<sub>V</sub>/E<sub>H</sub> Ratio</a>
</li>
</ul>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-lightingSolution"><div class="acnav__label acnav__label--level2 manufacturersInnerIcon">Circadian Lighting Solutions</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-lightingSystems">Lighting Systems</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-cctSystem">CCT System</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-desiredCCT">Desired CCT</a>
</li>
</ul>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-fixtures"><div class="acnav__label acnav__label--level2 manufacturersInnerIcon">Luminaires</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-retrofitVsNewDesign">Retrofit vs. New Design</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-retrofit">Retrofit</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-newDesign">New Design</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-fixtureTypes">Luminaire Type(s)</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-personalLightDevices">Personal Lighting Devices</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-beamDistribution">Intensity Distribution</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-orientationOffixtures">Orientation of Luminaire</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-mountingHeight">Mounting Height</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-maximumLumenOutput">Maximum Lumen Output</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-initialWattage">Initial Wattage</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-fixtureSpacing">Luminaire Spacing</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-spd">SPD</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-fixtureQuantity">Luminaire Quantity</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-lightLossFactors">Light Loss Factors</a>
</li>
</ul>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-computerDesign"><div class="acnav__label acnav__label--level2 manufacturersInnerIcon">Computer Design</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-lightingDesignSoftware">Lighting Design Software</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-iesFiles">.ies Files</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-csCalculator1">CS Calculator</a>
</li>
</ul>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-appliedDesign"><div class="acnav__label acnav__label--level2 manufacturersInnerIcon">Applied Design</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-illuminanceMeter">Illuminance Meter</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-spectroradiometer">Spectroradiometer</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-tapeMeasure">Tape Measure</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-installedFixtures">Installing Test Luminaires</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-controlSystem">Control System</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-daysimeter">Daysimeter</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-csCalculator2">CS Calculator</a>
</li>
</ul>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-results"><div class="acnav__label acnav__label--level2 manufacturersInnerIcon">Results</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-avgVerticalIlluminance">Avg Vertical illuminance</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-avgCSatOccupantLocation">Avg CS at Occupant Locations</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-avgHorizontalIlluminance">Avg Horizontal Illuminance</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-maximumLPD">Maximum LPD</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-energyUsage">Energy Usage</a>
</li>
</ul>
</li>
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-manufacturersSummary">Summary</a>
</li>
</ul>
</li>
<li id="occupants" class="acLevel1 has-children">
<div class="acnav__label occupantsIcon">Individuals</div>
<ul class="acnav__list acnav__list--level2">
<li>
<a class="acnav__link acnav__link--level2 section-link emptyIcon" href="#section-occupantsGeneralInformation">General Information</a>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-learnMore"><div class="acnav__label acnav__label--level2 occupantsInnerIcon">Learn More</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-occupantsLightingSystems">Lighting Systems</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-occupantsHorizontalIlluminance">Horizontal Illuminance</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-occupantsVerticalIlluminance">Vertical Illuminance</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-occupantsCCTSystem">CCT System</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-occupantsDesiredCCT">Desired CCT</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-csCalculator3">CS Calculator</a>
</li>
</ul>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-personalLightDevices"><div class="acnav__label acnav__label--level2 occupantsInnerIcon">Personal Lighting Devices</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-generalInformation">General Information</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-deskLuminaire">Desk Luminaire</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-lightGoggles">Light Goggles</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-lightTray">Light Tray</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-lightTable">Light Table</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-orangeFilterGoggles">Orange-tinted Glasses</a>
</li>
</ul>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-occupantsSummary">Summary</a>
</li>
</ul>
</li>
<li id="office" class="acLevel1 has-children">
<div class="acnav__label officeIcon">Offices</div>
<ul class="acnav__list acnav__list--level2">
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-officeGeneralInformation">General Information</a>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-officeOccupants"><div class="acnav__label acnav__label--level2 officeInnerIcon">Occupants</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-officeDaytimeWork">Daytime Work</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-officeEveningWork">Evening Work</a>
</li>
</ul>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-officeSpecialtyInformation">Specialty Information</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-officeSummary">Summary</a>
</li>
</ul>
</li>
<li id="healthcare" class="acLevel1 has-children">
<div class="acnav__label healthcareIcon">Healthcare</div>
<ul class="acnav__list acnav__list--level2">
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-healthcareGeneralInformation">General Information</a>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-healthcareOccupants"><div class="acnav__label acnav__label--level2 healthcareInnerIcon">Occupants</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-healthcareShiftWorkers">Shift Workers</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-healthcarePatients">Patients</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-healthcareInfants">Infants</a>
</li>
</ul>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-healthcareSpecialtyInformation"><div class="acnav__label acnav__label--level2 healthcareInnerIcon">Specialty Information</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-healthcareLightingInTheNICU">Lighting in the NICU</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-healthcarePatientOrientation">Patient Orientation</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-healthcareVisualPerformance">Visual Performance</a>
</li>
</ul>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-healthcareSummary">Summary</a>
</li>
</ul>
</li>
<li id="seniorcare" class="acLevel1 has-children">
<div class="acnav__label seniorcareIcon">Senior Care</div>
<ul class="acnav__list acnav__list--level2">
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-seniorcareGeneralInformation">General Information</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-seniorcareOccupants">Occupants</a>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-seniorcareSpecialtyInformation"><div class="acnav__label acnav__label--level2 seniorcareInnerIcon">Specialty Information</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-seniorcareReduceFalls">Lighting for Stability</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-seniorcareAlzheimersDisease">Alzheimer's Disease</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-seniorcareEyeDiseases">Eye Diseases</a>
</li>
</ul>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-seniorcareSummary">Summary</a>
</li>
</ul>
</li>
<li id="school" class="acLevel1 has-children">
<div class="acnav__label schoolIcon">Schools</div>
<ul class="acnav__list acnav__list--level2">
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-schoolGeneralInformation">General Information</a>
</li>
<li class="has-children">
<a class="section-link drop" href="#section-schoolOccupants"><div class="acnav__label acnav__label--level2 schoolInnerIcon">Occupants</div></a>
<ul class="acnav__list acnav__list--level3">
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-schoolPreteens">Pre-teens/Adolescents</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-schoolCollege">College</a>
</li>
<li>
<a class="acnav__link acnav__link--level3 emptyIcon subsection-link" href="#subsection-schoolSpecEd">Special Needs</a>
</li>
</ul>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-schoolSummary">Summary</a>
</li>
</ul>
</li>
<li id="additional" class="acLevel1 has-children">
<div class="acnav__label additionalIcon">Additonal Information</div>
<ul class="acnav__list acnav__list--level2">
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-about">About Us</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-ourMission">Our Mission, Role, and Values</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-acknowledgements">Acknowledgements</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-downloads">Downloads</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-glossary">Glossary</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-references">References</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-additionalResources">Additional Resources</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-sponsors">Sponsors</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-releaseNotes">Release Notes</a>
</li>
<li>
<a class="acnav__link acnav__link--level2 emptyIcon section-link" href="#section-suggestions">Suggestions/Report a Bug</a>
</li>
</ul>
</li>
</ul>
</div>
</nav>
</div>
</div>
<!-- Main Content -->
<div id="content" class="col-xl-9 col-lg-8 col-md-7 col-sm-12 p-0 mb-2 h-100-plus-offset overflow-auto">
<!-- Fundamentals -->
<article id="section-ourRole" class="article-fundamentals">
<div class="section-title text-center">
<h2>Our Role</h2>
</div>
<div class="container-fluid mt-4 pr-4 article-content">
<div class="row">
<div class="col-lg-6 col-md-12 text-center">
<figure><img data-src="img/background/fundamentals/our_role/1.png" class="lazy-load enlarge p-4 rounded w-100" alt="Research - Education - Application Diagram" /></figure>
</div>
<div class="col-lg-6 col-md-12 pr-0">
<figure><img data-src="img/background/fundamentals/our_role/2.png" class="lazy-load enlarge rounded w-100 mb-1 color-why" /></figure>
<figure><img data-src="img/background/fundamentals/our_role/3.png" class="lazy-load enlarge rounded w-100 mb-1 color-what" /></figure>
<figure><img data-src="img/background/fundamentals/our_role/4.png" class="lazy-load enlarge rounded w-100 mb-1 color-who" /></figure>
<figure><img data-src="img/background/fundamentals/our_role/5.png" class="lazy-load enlarge rounded w-100 mb-1 color-how" /></figure>
</div>
</div>
</div>
</article>
<article id="section-whatIsLight" class="article-fundamentals">
<div class="section-title text-center">
<h2>What is Light?</h2>
</div>
<div class="container-fluid mt-4 article-content">
<div class="row">
<div class="col">
<figure class="float-right w-50 m-4 mobile-figure">
<img data-src="img/background/fundamentals/what_is_light/1.png" class="lazy-load enlarge w-100 drop-shadow rounded p-4 pl-0" />
<figcaption class="figcaption text-center mt-3">Adapted from Human Factors in Lighting (Second Edition, p.4), by Peter R. Boyce, 2003, London: Taylor & Francis. Copyright 2003 by Peter R. Boyce.</figcaption>
</figure>
<p>
Light is the portion of the electromagnetic spectrum between about 380 and 780 nanometers (nm) that evokes a visual response in humans, and is the only quantity of the physical world that is defined entirely in terms of the human sensory mechanism. But light isn’t just for vision. The pattern of light and dark incident on the retinae also provides timing cues that inform and synchronize the <a data-termID="8" class="term">circadian systems</a> of Earth’s innumerable organisms, from bacteria, plants, and fungi through insects and amphibians to mammals and humans. In humans, light also evokes an acute alerting response any time of day or night. In this context, it is important to understand that “acute” connotes a short-term (< 24 hours) effect that is largely independent of the circadian system <a data-refID="1" class="ref"></a> rather than an effect that is simply sudden, sharp, or severe.
</p>
</div>
</div>
</div>
</article>
<article id="section-lightingAndtheCircadianSystem" class="article-fundamentals">
<div class="section-title text-center">
<h2>Light and the Circadian System</h2>
</div>
<div class="container-fluid mt-4 pr-4">
<div class="row">
<div class="col">
<figure class="float-right w-50 mobile-figure">
<img data-src="img/background/fundamentals/lighting_and_the_circadian_system/1.png" class="lazy-load enlarge drop-shadow p-4 m-4 pl-0 rounded w-100" />
<figcaption class="figcaption text-center">Watch this video to learn more about <a target="_blank" href="https://www.youtube.com/watch?v=noJnpGmWEPk&list=PL_X9RKGy9RIZmgzoJwHZsQmpPW6O1fLu3&index=1">circadian rhythms</a></figcaption>
</figure>
<p>
The 24-hour pattern of light and dark that accompanies Earth’s axial rotation regulates the physiology and behavior of almost every living thing on the planet. For humans, light reaching the back of our eyes is the primary exogenous (external) cue that synchronizes or entrains the body’s endogenous (internal) <a data-termID="32" class="term">master biological clock</a> and thus our <a data-termID="7" class="term">circadian rhythms</a> to the solar day, essentially telling our bodies to do the right thing at the right time. Other secondary exogenous cues include social activity <a data-refID="2" class="ref"></a>, meal times <a data-refID="3" class="ref"></a>, and physical activity <a data-refID="4" class="ref"></a>, among others. Sleeping and waking, feeding and fasting, the regulation of core body temperature, blood pressure, and the secretion of hormones are just a few examples of circadian rhythms. The term “circadian,” coined by biologist Franz Halberg in 1959, is a blended word derived from the Latin circa (“about”) and dies (“day”).
</p>
<figure class="mobile-figure"><img data-src="img/background/fundamentals/lighting_and_the_circadian_system/2.png" class="lazy-load enlarge float-left w-45 drop-shadow rounded p-4 mr-4 mt-4 mb-4 ml-0" /></figure>
<p>
Because the human <a data-termID="8" class="term">circadian system</a> <a data-termID="54" class="term">free-runs</a> at an average period of about 24.2 hours—slightly longer than the solar day—a daily cue of light and dark is required to advance the circadian system by about 10–15 minutes, thereby continually resetting the biological clock to maintain <a data-termID="5" class="term">circadian entrainment</a> <a data-refID="5" class="ref"></a>. But what light gives, light can also take away.
</p>
<p>
Exposure to light at the wrong time, or not receiving enough light at the right time, has become increasingly common since the advent of electrical lighting over a century ago. Exposure to light at night (LAN), and even a complete reversal of the day–night pattern in the case of night-shift workers, are now facts of life in our 24-hour society. But exposure to light at night and insufficient exposure to light early in the day has been linked with poor sleep and a host of health and behavioral problems. Long-term disruption of the daily cycle of light and dark can lead to chronic disruption of the circadian system, which has been associated with metabolic dysregulation (leading to weight gain, obesity, and type 2 diabetes) <a data-refID="6" class="ref"></a>, certain forms of cancer <a data-refID="7" class="ref"></a>, depression <a data-refID="8" class="ref"></a>, and other maladies <a data-refID="9" class="ref"></a>.
</p>
</div>
</div>
<div class="row">
<div class="col">
<h4 class="text-center mb-4">Four characteristics of light and light exposures play crucial roles in the circadian system’s response:</h4>
</div>
</div>
<div class="row">
<div class="col-md-6">
<b>1. The amount or level of light received at the eyes.</b>
<figure class="float-left w-100 mobile-figure"><img data-src="img/background/fundamentals/lighting_and_the_circadian_system/3.png" class="lazy-load enlarge w-100 rounded p-4" alt="Lighting and The Circadian System 3" /></figure>
</div>
<div class="col-md-6">
<p>
Early circadian research in animal <a data-refID="10" class="ref"></a><a data-refID="11" class="ref"></a> and human <a data-refID="12" class="ref"></a><a data-refID="13" class="ref"></a> models found that varying light levels at the eyes differentially affect the nighttime suppression of the hormone <a data-termID="33" class="term">melatonin</a> (the release of which prepares the body for sleep) and the timing of circadian phase (i.e., either advancing or delaying the timing of the circadian system’s 24-h cycle). The greater the amount of light, in other words, the greater the melatonin suppression and the greater the advance/delay (or shift) in circadian phase.
</p>
</div>
</div>
<div class="row">
<div class="col-md-6">
<b>2. The spectral properties of the light experienced.</b>
<figure class="float-left w-100 mobile-figure"><img data-src="img/background/fundamentals/lighting_and_the_circadian_system/4.png" class="lazy-load enlarge w-100 rounded p-4" alt="Lighting and The Circadian System 4" /></figure>
</div>
<div class="col-md-6">
<p>
Because it has a peak spectral sensitivity that occurs around 460 nm <a data-refID="14" class="ref"></a><a data-refID="15" class="ref"></a>, the human circadian system is maximally sensitive to short-wavelength (“bluish”) light (e.g., 465–475 nm), which in turn is maximally effective for stimulating the circadian system. In a manner similar to differences in light levels, short-wavelength light suppresses melatonin to a greater degree than longer wavelength (“reddish”) light (peak wavelength around 550 nm) and if experienced in the evening will delay circadian phase. Long-wavelength light, on the other hand, provides minimal circadian stimulus (CS) and thus only nominally suppresses melatonin and does not affect circadian phase. Because light of all wavelengths evokes an alerting response at any time of day or night, long-wavelength light is especially useful for promoting alertness during the afternoon and evening without disrupting the circadian system <a data-refID="16" class="ref"></a><a data-refID="17" class="ref"></a>.
</p>
</div>
</div>
<div class="row">
<div class="col-md-6">
<b>3. The timing and duration of light exposures.</b>
<figure class="float-left w-100 mobile-figure"><img data-src="img/background/fundamentals/lighting_and_the_circadian_system/5.png" class="lazy-load enlarge w-100 rounded p-4" alt="Lighting and The Circadian System 5" /></figure>
</div>
<div class="col-md-6">
<p>
Humans are far more sensitive to light stimulus at night than in the middle of the day <a data-refID="18" class="ref"></a><a data-refID="19" class="ref"></a>. Experiencing high levels of light later in the day and in the evening will delay circadian phase, causing us to fall asleep later than our usual bedtime, leading us to sleep-in or feel tired on waking the next day. Conversely, experiencing high levels of short-wavelength light early in the morning will reset the master biological clock, advancing our circadian phase and helping to entrain our circadian system to the solar day. Again, because the circadian system free-runs at a period that is longer than the solar day, we need light early in the day to maintain regular bedtimes. Longer exposure durations are also more effective at suppressing melatonin <a data-refID="20" class="ref"></a>.
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<b>4. </b> <b>A person’s history of light exposures.</b>
<figure class="w-100 text-center mobile-figure"><img data-src="img/background/fundamentals/lighting_and_the_circadian_system/6.png" class="lazy-load enlarge text-center w-85 rounded p-4" alt="Lighting and The Circadian System 6" /></figure>
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While it is well-accepted that exposure to higher light levels results in greater melatonin suppression at night, research also shows that a one-day light exposure of 200 lux suppresses melatonin to a greater degree when it is preceded by 3 days of dim light (< 1 lux) compared to 3 days of the same 200-lux source <a data-refID="21" class="ref"></a>. While the visual system’s response to light is virtually instantaneous, the circadian system’s response to light is cumulative <a data-refID="22" class="ref"></a>.
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When appropriately specified according to these four characteristics, light exposures can be tailored to remedy symptoms of seasonal affective disorder <a data-refID="23" class="ref"></a>, increase sleep efficiency in older adults (including those with Alzheimer’s disease) <a data-refID="24" class="ref"></a><a data-refID="25" class="ref"></a><a data-refID="26" class="ref"></a>, promote circadian rhythmicity in premature infants <a data-refID="27" class="ref"></a>, increase alertness at all times of day and night <a data-refID="28" class="ref"></a><a data-refID="29" class="ref"></a><a data-refID="30" class="ref"></a>, and improve alertness and selected measures of performance <a data-refID="31" class="ref"></a><a data-refID="32" class="ref"></a>.
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Here are two examples of disruptive and entraining lighting schemes. Typical commercial and residential lighting systems are considered to be inadequate for meeting the needs of the circadian system.
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<h3 class="text-center text-danger"><i class="fas fa-times"></i> Disruptive Lighting Scheme</h3>
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<h6 class="card-subtitle mb-2 ml-2 text-muted">- Light level and spectrum are inadequate for stimulating the circadian system <br />- Circadian system free-runs on average period of 24.2 hours <br />- The biological clock is out of sync with the 24-hour solar day<br /><small class="ml-2">(The timing of the circadian phase delay shown in the graphic is exaggerated for effect.)</small></h6>
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<h5>Short Term Effects</h5>
<h6 class="card-subtitle mb-4 ml-2 text-muted">- Sleep deprivation <br />- Poor mood/behavior <br />- Reduced performance/productivity <br />- Lack of alertness</h6>
<h5>Long Term Effects</h5>
<h6 class="card-subtitle mb-4 ml-2 text-muted">- Cardiovascular and metabolic disease <br />- Obesity <br />- Some forms of cancer <br />- Depression</h6>
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<h3 class="text-center text-success"><i class="fas fa-check"></i> Entraining Lighting Scheme</h3>
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<h6 class="card-subtitle mb-2 ml-2 text-muted">- Bright light levels stimulate the circadian system in the morning hours, while dimmer evening light promotes a robust light/dark pattern for the circadian system <br />- Tunable <a data-termID="50" class="term">white light</a> going from cool in the morning to warm in the evening further enhances a robust scheme <br />- 24.2-hour biological clock becomes entrained to 24-hour solar day</h6>
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<h5>Short Term Effects</h5>
<h6 class="card-subtitle mb-4 ml-2 text-muted">- Improved sleep <br />- Better mood/behavior <br />- Improved performance <br />- Acute alertness</h6>
<h5>Long Term Effects</h5>
<h6 class="card-subtitle mb-4 ml-2 text-muted">- Improved cardiovascular and metabolic health <br />- Resistance to depression <br />- Resistance to obesity <br />- Reduced </h6>
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<article id="section-theSleepWakeCycle" class="article-fundamentals">
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<h2>The Sleep/Wake Cycle</h2>
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The human body’s nervous and endocrine systems transmit information throughout the body to regulate all bodily functions. The nervous system is essentially a hard-wired network made up of over 100,000 million nerve cells that transmit electrical signals from the body’s peripheral nervous system and the outside world through the spinal cord to the brain (the central nervous system), which in turn dispatches electrical signals to direct the actions of the body’s muscles, organs, and tissues. The endocrine system, on the other hand, sends chemical signals through the bloodstream in the form of hormones excreted by the body’s endocrine glands to regulate processes such as the sleep/wake cycle.
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Secretion of the hormones <a data-termID="33" class="term">melatonin</a> and cortisol both follow <a data-termID="7" class="term">circadian rhythms</a> that are regulated by inputs from the suprachiasmatic nuclei (SCN) of the brain’s anterior hypothalamus, also known as the <a data-termID="32" class="term">master biological clock</a>, based on cues provided by the patterns of light and dark received at the retinae <a data-refID="33" class="ref"></a> <a class="segue" href="#section-nonVisualSystems">(see Non-visual Systems)</a>. Melatonin, known as the “darkness hormone” because it is released at night and under conditions of darkness, is produced by the pineal gland and prepares the body for sleep <a data-refID="34" class="ref"></a>. Melatonin concentration in the bloodstream begins to diminish in the latter hours of sleep and remains barely detectable throughout the day.
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Cortisol, produced by the adrenal glands, promotes the synthesis and storage of glucose and influences metabolic, immune, muscle, and functions <a data-refID="35" class="ref"></a> as well as various brain activities as cognitive function <a data-refID="36" class="ref"></a> and the regulation of emotions <a data-refID="37" class="ref"></a>. In humans, it remains in low concentration in the bloodstream throughout the day but gradually elevates throughout the night, culminating 30–45 minutes after waking in a sharp increase known as the <a data-termID="13" class="term">cortisol awakening response (CAR)</a> <a data-refID="38" class="ref"></a><a data-refID="39" class="ref"></a>. Research indicates exposure to polychromatic <a data-termID="50" class="term">white light</a> at morning awakening enhances the CAR in adults who are not sleep restricted, while awakening in darkness or dim light reduces the CAR’s dynamic <a data-refID="40" class="ref"></a><a data-refID="41" class="ref"></a><a data-refID="42" class="ref"></a>. Our understanding of cortisol and its response to light are not as well understood as that of melatonin <a data-refID="41" class="ref"></a><a data-refID="42" class="ref"></a><a data-refID="43" class="ref"></a>. It has been speculated that the CAR promotes alertness and arousal in anticipation of the forthcoming day’s demands <a data-refID="44" class="ref"></a><a data-refID="45" class="ref"></a><a data-refID="46" class="ref"></a>.
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<img data-src="img/background/fundamentals/sleep_pressure_and_daily_alertness/1.png" alt="Sleep Pressure and Daily Alertness 1" class="lazy-load enlarge w-100 drop-shadow p-4 rounded" />
<figcaption class="figcaption text-center mt-3">Adapted from “Circadian and Sleep-Wake Dependent Impact on Neurobehavioral Function,” by C. Cajochen and K. Blatter, 2004, Psychologica Belgica, 44-1/2, p. 59-80, Figure 3.</figcaption>
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The regulation of sleep and waking has been broadly conceptualized as a two-process model involving interaction between a <a data-termID="23" class="term">homeostatic</a> process, which maintains stability by counteracting opposing forces or influences, and a process driven by the circadian pacemaker <a data-refID="47" class="ref"></a><a data-refID="48" class="ref"></a><a data-refID="49" class="ref"></a>. The homeostatic process, known variously as Process S, or simply “sleep debt,” is a natural tendency toward sleep that accumulates during our waking hours and declines while we sleep. This tendency is counteracted to maintain daytime wakefulness by an alerting signal that is regulated by the <a data-termID="8" class="term">circadian system</a>, called Process C. Experiments using animals whose circadian rhythms have been disrupted by surgical lesions on the SCN have shown that Process S is not affected, suggesting that the two processes are independently regulated despite whatever “crosstalk” might occur between them <a data-refID="49" class="ref"></a>.
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<figure class="text-center mobile-figure"><img data-src="img/background/fundamentals/sleep_pressure_and_daily_alertness/2.png" alt="Sleep Pressure and Daily Alertness 2" class="lazy-load enlarge float-right w-25 rounded p-0 m-3" /></figure>
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The functioning of the two-process sleep model should be familiar to anyone who has experienced fatigue during the workday. Around 2–4 PM, or 16–18 hours after the previous night’s bedtime, many people experience a decline in alertness and performance known as the <a data-termID="41" class="term">post-lunch dip</a>. At this time of day, Process C cannot completely counteract Process S, which is gathering momentum prior to its abrupt peak and decline about 8 hours later, triggering sleep. The LRC has innovated a unique application for getting us through the post-lunch dip by using light to promote acute alertness, providing an effect that is similar to a cup of coffee. Process C reaches its peak early evening (also known as wake maintenance zone), when falling asleep is very difficult (some refer this time as their “second wave”). After reaching its peak, Process C switches to sending the body a sleeping signal; together with the high sleep debt, sleep is triggered.
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<article id="section-theEye" class="article-fundamentals">
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<h2>The Eye</h2>
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<img data-src="img/background/fundamentals/structure_of_the_eye/1.png" alt="Structure of the Eye 1" class="lazy-load enlarge w-100 rounded p-4 drop-shadow" />
<figcaption class="figcaption text-center mt-3">Adapted from Human Factors in Lighting (Second Edition, p.48), by Peter R. Boyce, 2003, London: Taylor & Francis. Copyright 2003 by Peter R. Boyce.</figcaption>
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The eye is a remarkable, complex structure that gathers electromagnetic radiation from the environment, transforms it into electrical signals through a process known as phototransduction, and relays visual information to lateral geniculate nucleus (LGN) in the brain via the optic nerve. Phototransduction occurs in the relatively tiny, innermost layer of the eye, the retina. Most of the eye is filled with fluid, consisting of the aqueous humor in the front portion of the eye and the vitreous humor that composes the far larger, interior portion of the eye. The clear, watery aqueous humor provides nutrients to the eye’s cornea and lens, while the vitreous humor helps to maintain the eye’s shape and remove any material that might block the incoming light.
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<p>
Light entering the eye is bent (or refracted) by the cornea and the double-convex crystalline lens, which together focus light on the retina’s surface. While not having the refractive power of the cornea, the lens can make finer adjustments to sharply focus light from varying distances. For focusing light from distant objects on the retina, the lens is flattened and thinned (or “unaccommodated”); for closer objects, the lens is made thicker and rounder (or “accommodated”) by the action of the ciliary muscle that surrounds the lens in a ring. The clarity of images on the retina is also influenced by the pupil and iris, which expand and contract to regulate the light entering the lens, thereby adjusting the image’s depth of field and reducing aberrations that can be caused by light passing through the outer, thinner edges of the lens.
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<article id="section-theRetina" class="article-fundamentals">
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<h2>The Retina</h2>
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Unlike the other components of the eye, the retina is considered an extension of the brain. The retina is composed of three major layers containing five types of neurons, from back to front: (1) the outer nuclear layer containing the <a data-termID="40" class="term">photoreceptors</a> (i.e., <a data-termID="42" class="term">rods</a> and <a data-termID="9" class="term">cones</a>); (2) the inner nuclear layer containing the bipolar, horizontal, and amacrine cells; and (3) the ganglion cell layer. Two intervening structures called the outer and inner plexiform layers enable connections (or <i>synapses</i>) between these three layers of cells.
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<img data-src="img/background/fundamentals/structure_of_the_retina/1.png" alt="Structure of the Retina 1" class="lazy-load enlarge w-100 p-4 drop-shadow rounded" />
<figcaption class="figcaption text-center mt-3">Adapted from Human Factors in Lighting (Second Edition, p.49), by Peter R. Boyce, 2003, London: Taylor & Francis. Copyright 2003 by Peter R. Boyce.</figcaption>
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The human retina is known to be inverted, which means that the photoreceptors are located in the distant part of the layer, opposite to where light enters the eye. Once it hits the photoreceptor layer, light is absorbed by the “classical” photoreceptors (i.e., the rods and cones). Light that is not absorbed by the photoreceptors is absorbed by the pigment epithelium, which is positioned at the very back of the retina behind the photoreceptors and prevents reflection of light back in the direction from which it came (known as <i>backscattering</i>). The photoreceptors provide input to the bipolar cells with the help of the horizontal cells, and the bipolar cells in turn provide input to the ganglion cells with the help of the amacrine cells. Finally, visual signals are passed by the axons of the ganglion cells that thread across the nerve fiber layer at the front of the retina to the optic disk, where they combine to form the optic nerve that transmits signals to several targets in the brain.
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<article id="section-rodsAndCones" class="article-fundamentals">
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<h2>Rods and Cones</h2>
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The two “classical” types of <a data-termID="40" class="term">photoreceptor</a>, <a data-termID="42" class="term">rods</a> and <a data-termID="9" class="term">cones</a>, have different sensitivities, connections to other retinal cells, and distributions across the retina. Rods have very low spatial resolution but are very sensitive to light, especially at low levels. Cones, on the other hand, are very effective at discriminating details but are much less sensitive to light. The rod-mediated perception of light is called scotopic vision, which has an upper activation threshold in dim light levels that are roughly equivalent to the luminance of a white piece of paper in starlight <a data-refID="50" class="ref"></a>. Cone-mediated perception of light is known as photopic vision, which is activated at high light levels <a data-refID="50" class="ref"></a>. Mesopic vision lies in a middle range between the two in which both rods and cones are active, in conditions such as starlight and moonlight.
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<figure class="float-right w-35 mb-4 mx-4 mt-0 mobile-figure">
<img data-src="img/background/fundamentals/structure_of_the_retina/2.png" alt="Structure of the Retina 2" class="lazy-load enlarge w-100 p-4 drop-shadow rounded" />
<figcaption class="figcaption text-center mt-3"> Adapted from Circadian Physiology (Second Edition, p.453), by Roberto Refinetti, 2006, Florida: CRC Press and Taylor & Francis Group. Copyright 2006 by Taylor & Francis Group, LLC.</figcaption>
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Unlike rods, which contain a single photopigment, there are three types of cones, each containing one photopigment that permits the perception of color, which is formed in the brain, not at the photoreceptors. In this way, color is a pigment of our imagination. Each of the photopigments has its own peak sensitivity to light of different wavelengths and is favored by separate classes of cones. Accordingly, these classes of cones are labelled: short (S-cones), with a peak spectral sensitivity (after lens absorption) at 445 nm; medium (M-cones), with a peak spectral sensitivity at 535 nm; and long (L-cones), with a peak spectral sensitivity at 570 nm. On average, the human retina contains about 92 million rods and 4.6 million cones <a data-refID="51" class="ref"></a>. Although the numerical distribution of cone classes can vary widely between individuals, a typical ratio of L:M:S cones has been estimated to be 32:16:1 <a data-refID="52" class="ref"></a>.
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<img data-src="img/background/fundamentals/rods_and_cones/1.png" alt="Rods and Cones 1" class="lazy-load enlarge w-100 p-4 drop-shadow rounded" />
<figcaption class="figcaption text-center mt-3">Adapted from “How is Color Blindness diagnosed?” by Daniel Georgiev.</figcaption>
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Because they outnumber cones by 20:1, rods are found at greater densities throughout most of the retina. This spatial relationship is inverted in a tiny (about 1 mm in diameter), specialized “pit” in the central retina known as the fovea, where the cone density is almost 200 times greater at its center than elsewhere in the retina and where rods are entirely absent. The fovea mediates a high degree of <a data-termID="49" class="term">visual acuity</a> that rapidly drops off just a few degrees from the line of sight (i.e., the center of the fovea at 0°), as shown in the graphic above. It should be noted that only L- and M-cones are found at the very center of the fovea.
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<img data-src="img/background/fundamentals/rods_and_cones/2.png" alt="Rods and Cones 2" class="lazy-load enlarge w-100 p-4 drop-shadow rounded" />
<figcaption class="figcaption text-center mt-3">Adapted from Illuminating Engineering Society, The Lighting Handbook (Tenth Edition, p.2.6), by David L. DiLaura, Kevin W. Houser, Richard G. Mistrick, and Gary R. Steffy, 2011, New York: Illuminating Engineering Society. Copyright 2011 by the Illuminating Engineering Society of North America.</figcaption>
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This differential distribution of rods and cones explains why we can only see very dim star constellations in the nighttime sky with our <a data-termID="37" class="term">peripheral vision</a>, which is mediated by the rod-rich zones of the peripheral retina. Attempting to directly focus on the stars and distinguish them from the dark sky causes the incoming light to fall on the cone-rich fovea and surrounding macula lutea, which comprise the retinal zone responsible for <a data-termID="52" class="term">central vision</a> and are only activated by much higher light levels. The same situation holds for color vision in our visual adaptation to our surroundings at night.
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</article>
<article id="section-nonVisualSystems" class="article-fundamentals">
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<h2>Non-visual Systems</h2>
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In addition to relaying image-forming (“visual”) signals processed by the <a data-termID="42" class="term">rods</a> and <a data-termID="9" class="term">cones</a>, the retina’s ganglion cells transmit signals via the optic nerve to several targets in the brain that control non-image-forming (“non-visual”) functions such as: (1) the pupillary light reflex (i.e., expanding and contracting of the pupil in response to changing light levels), (2) the coordination of head and eye movement for tasks such as reading or watching sports, and (3) <a data-termID="8" class="term">circadian system</a> response. In circadian system response, a unique class of retinal ganglion cells known as <a data-termID="29" class="term">intrinsically photosensitive retinal ganglion cells (ipRGCs)</a> send light–dark neural signals to the SCN (the circadian system’s <a data-termID="32" class="term">master biological clock</a>) along a neurological pathway known as the retinohypothalamic tract (RHT). Only relatively recently discovered <a data-refID="53" class="ref"></a>, the ipRGCs play a key—but not exclusive—role in <a data-termID="5" class="term">circadian entrainment</a>. The circadian system’s differential spectral sensitivity to various wavelengths of light, particularly its peak spectral sensitivity at 460 nm, suggests at the very least that the S-cone photoreceptors are also involved circadian phototransduction.
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<figure class="text-center mobile-figure"><img data-src="img/background/fundamentals/iprgc_photoreceptors/1.png" alt="ipRGC 1" class="lazy-load enlarge float-right w-90 m-4 p-2 drop-shadow rounded" /></figure>
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<figure class="text-center mobile-figure"><img data-src="img/background/fundamentals/visual_vs_non-visual_system/1.png" alt="Visual vs. Non-visual System 1" class="lazy-load enlarge float-right w-90 m-4 drop-shadow rounded" /></figure>
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<article id="section-whatIsCircadianLighting" class="article-fundamentals">
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<h2>What is Circadian Lighting?</h2>
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Watch this video to learn more about <a href="https://www.youtube.com/watch?v=wxXxpnCOpSU&list=PL_X9RKGy9RIZmgzoJwHZsQmpPW6O1fLu3&index=3&t=0s" target="_blank"> circadian stimulus</a>.
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Watch this video to learn about the <a target="_blank" href="https://www.youtube.com/watch?v=8poiwxTFKms&list=PL_X9RKGy9RIZmgzoJwHZsQmpPW6O1fLu3&index=9">future direction in circadian light for health</a>.
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Researchers at the LRC have proposed a 24-hour lighting scheme for promoting <a data-termID="5" class="term">circadian entrainment</a> that maximizes <a data-termID="14" class="term">circadian stimulus (CS)</a> during the day, minimizes CS at night, and maintains appropriate levels of light for visual performance at all times <a data-refID="22" class="ref"></a><a data-refID="54" class="ref"></a><a data-refID="55" class="ref"></a>. Field and laboratory research <a data-refID="56" class="ref"></a><a data-refID="57" class="ref"></a><a data-refID="58" class="ref"></a><a data-refID="59" class="ref"></a> suggests that delivering high CS (at least 0.3, and preferably ≥ 0.4) during the day can be achieved by providing about 500 lux (at the eye) of a <a data-termID="50" class="term">white light</a> source (ranging from 2700-5000 K). Relatively dim (< 30 lux at the eye) <a data-termID="1" class="term">ambient lighting</a> providing low CS (< 0.1) during the evening can be achieved using any white light source.
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<figure class="text-center mobile-figure">
<img data-src="img/background/fundamentals/what_is_circadian_lighting/4.png" alt="What is Circadian Lighting 2" class="lazy-load enlarge w-40 p-4 m-4 drop-shadow rounded float-left" />
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The lighting conditions described on this website are specified in terms of <a data-termID="12" class="term">correlated color temperature (CCT)</a> and light level (i.e., photopic illuminance) to provide targeted amounts of <a data-termID="6" class="term">circadian light (CL<sub>A</sub>)</a> <a data-refID="60" class="ref"></a> and CS at participants’ eyes <a data-refID="61" class="ref"></a><a data-refID="62" class="ref"></a><a data-refID="63" class="ref"></a>. Lighting designs universally require illuminance measurements on the horizontal and vertical planes. Briefly, Illuminance (E) is the amount of luminous flux incident on a surface <a data-refID="64" class="ref"></a>, and is measured in lumens per square meter (lux) or lumens per square foot (footcandle). One footcandle is equal to approximately 11 lux. The CL<sub>A</sub> metric is irradiance weighted by the spectral sensitivity of the retinal phototransduction mechanisms stimulating the response of the <a data-termID="2" class="term"> biological clock</a>, based on nocturnal <a data-termID="33" class="term">melatonin</a> suppression. The CS metric is a transformation of CL<sub>A</sub> into a relative scale from approximately 0.1 (≈ 10%), the threshold for <a data-termID="8" class="term">circadian system</a> activation, to approximately 0.7 (≈ 70%), response saturation, and is equivalent to nocturnal melatonin suppression in percent after a 1-h exposure to light. Although the photopic luminous efficiency function (V(λ)) used to convert radiant power (Watts) into photopic lux is not the correct efficiency function for the circadian system response, it will be used throughout this website because of its widespread use by the lighting community.
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<img data-src="img/background/fundamentals/what_is_circadian_lighting/3.png" alt="What is Circadian Lighting 2" class="lazy-load enlarge w-40 p-4 m-4 drop-shadow rounded float-right" />
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<p>
The accompanying graph shows the absolute sensitivity of the human circadian system to light measured in units of CS, as a function of circadian light, measured in terms of CL<sub>A</sub>. The shaded portions of the graph illustrate typical levels of illumination found outdoors at night, indoors in homes at night, indoors in offices, and outdoors during the daytime. Also shown is the relationship between photopic illuminance for daylight and incandescent spectra at different levels of CL<sub>A</sub> and thus CS.
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High circadian stimulation during the day and low circadian stimulation during the evening can be achieved using a combination of daylight and electric light sources. Daylight can certainly be an effective light source for regulating the circadian system. Outdoor lighting has the ideal quantity, spectrum, distribution, timing, and duration, but it should not be assumed that daylight in buildings will always provide people with a suitable circadian light pattern. Again, a quantitative analysis of daylight in the space should be carefully made because the amount of daylight varies considerably throughout a building. Daylight levels in a room drop very quickly as the distance from the window increases; daylight levels are quite low 3-4 meters away from a window, even on a sunny day. It should also be noted that if sunlight from the window penetrates the room, discomfort glare may cause occupants to draw blinds or shades, eliminating daylight entirely from the space. Since it cannot be assumed that daylight in buildings is always going to be a solution for circadian entrainment, electric light must always be considered.
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Throughout the day, the dynamic cycle of daylight spans a broad range of CCTs and light levels. Sunrise is characterized by warm, diffuse 2000 K light that transitions to somewhat cooler 3500 K light by the early morning, while the late morning and afternoon see 6000 K light on cloudy days and 10000 K light on clear, blue-sky days. These lighting conditions are mirrored for the remainder of the day, leading to dusk and darkness. Illuminance levels over the entire 24-hour solar cycle can range from as low as about 0.001 lux for starlight and 0.2 lux for moonlight on a clear night to about 10,000 lux on an overcast day and more than 100,000 lux on a clear, blue-sky day <a data-refID="65" class="ref"></a>. The CS exposures for these daylight conditions range from negligible (CS < 0.01) in starlight to full saturation (CS ≈ 0.7) at midday.
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<img data-src="img/background/fundamentals/what_is_circadian_lighting/1.png" alt="What is Circadian Lighting 1" class="lazy-load enlarge w-65 p-2 rounded text-center" />
<figcaption class="figcaption text-center mt-3">Adapted from Illuminating Engineering Society, The Lighting Handbook (Tenth Edition, p.7.5), by David L. DiLaura, Kevin W. Houser, Richard G. Mistrick, and Gary R. Steffy, 2011, New York: Illuminating Engineering Society. Copyright 2011 by the Illuminating Engineering Society of North America.</figcaption>
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The natural cycle of daylight is optimal for circadian entrainment, but few spaces in the built environment afford sufficient access to windows for providing daylight conditions and some spaces have no access to windows at all. In absence of adequate daylight, electric lighting can be specified and designed to mimic the cycle of the solar day, providing a dynamic schedule of varying CCTs and light levels with <a data-termID="31" class="term">luminaire</a> spacing and light <a data-termID="28" class="term">intensity distribution</a> that effectively deliver light to the occupants’ eyes.
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If a <a data-termID="20" class="term">dynamic CCT</a> system is unavailable or impractical, a <a data-termID="16" class="term">CS schedule</a> can nonetheless be achieved using a fixed CCT and variable light levels to provide a robust light/dark schedule. Since cool-CCT light sources (6500 K or 5000 K) have higher spectral power in the short-wavelengths (‘blue’ light) (450-485 nm), they deliver about twice the amount of CS than low-CCT sources (e.g., 2700 K or 3000 K) for the same photopic light levels at the eye. This means that cool sources require lower output to meet desirable CS targets for circadian lighting, and warmer sources require greater output. But when properly specified, virtually any lighting system—either warm or cool—can deliver appropriate levels of CS to synchronize our biological clocks with the solar day.
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If overhead lighting cannot provide enough light to the eye to deliver the appropriate CS levels, several other strategies are at your disposal. Personal desk lamps or other luminous devices are a good alternative for delivering extra light, especially in the morning. It is most important to provide a minimum CS level of 0.3 at this time of day to promote circadian entrainment. If available, daylight through a window can also supplement overhead electric lighting to provide effective levels of CS, with some qualifications. But by nature, daylight is a variable source of illuminance and CS, especially in the built environment. Seasonal changes, for example, strongly influence daylight availability. What may be perfect in early May could be unbearable in July—causing occupants to close their window shades to eliminate discomfort glare and thus eliminate any daylight benefit—and woefully inadequate by mid-December. The distance between a window and the occupants’ eyes is also a crucial concern, since daylight levels drop as the distance increases. In fact, light levels can be very low at modest distances of as little as 10–12 feet (3-3.66 m), even on a sunny day. In any case, the bottom line is that a quantitative analysis must be made that accounts for all light in the space, whether from overhead luminaires, desktop devices, or windows.
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Your computer screens can deliver a certain amount of CS that can be added to the overhead lighting, but, as with daylight, different screen types and sizes will deliver different CS levels, so it would be best to plan to achieve the targeted CS without the use of screens.
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<h2>Summary</h2>
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