{"id":223,"date":"2014-10-04T14:44:01","date_gmt":"2014-10-04T18:44:01","guid":{"rendered":"https:\/\/designinglight.com\/?p=223"},"modified":"2014-10-04T14:44:01","modified_gmt":"2014-10-04T18:44:01","slug":"circadian-lighting","status":"publish","type":"post","link":"https:\/\/designinglight.com\/?p=223","title":{"rendered":"Circadian Lighting"},"content":{"rendered":"

A recent article<\/a> in The Wall Street Journal discussed the possibilities and benefits of lighting systems that shift color to mimic the changes in daylight. It\u2019s a complicated subject so it\u2019s not surprising that some of what\u2019s reported is inaccurate, so let me clarify a few things.<\/p>\n

First, our current understanding of how light affects our circadian rhythms is that a light activates a type of cell in the retina called intrinsically photosensitive retinal ganglion cells (ipRGC). These cells, unlike rods and cones, are unrelated to vision. The signal they send to the brain is received by the suprachiasmatic nucleus (SCN), which is the body\u2019s hormone regulator. As the graph below illustrates, the ipRGCs are most sensitive to short wavelength (blue) light and, unlike rods and cones, are unaffected by long wavelength (red) light. (A more detailed explanation can be found in Chapter 16 of Designing With Light<\/em>, and in this article<\/a> from the Journal of Circadian Rhythms.)<\/p>\n

 <\/p>\n

\"ipRGC<\/a>
ipRGC (black), rod (blue), and cone (red) sensitivity curves<\/figcaption><\/figure>\n

 <\/p>\n

The ipRGCs signal to the SCN, which keeps our circadian rhythms are kept in sync with the day\/night cycle, seems to be affected by three factors: color balance; intensity; timing. Cool (bluish) light should be delivered at a relatively high brightness in the morning hours. Delivering cool light in the evening hours can disrupt sleep and other processes controlled by the SCN.<\/p>\n

Next, there\u2019s nothing special about LED lighting that makes it uniquely appropriate for this application. Fluorescent, HID, and incandescent light (adjusted with color filters) can all be used to create a system that delivers cool light in the morning and warm light in the evening. In all cases, this involves the use of light sources of several tints (warm, cool, and possibly neutral) that are individually controlled. The WSJ is completely wrong when it says \u201cunlike incandescent or fluorescent lights, LED lights’ materials and electronic components allow for finer adjustments of color, brightness and intensity.\u201d A single LED creates light of a single color. To shift colors a second LED is required. Brightness and intensity are the same thing. With LEDs set to surpass sales of all other light sources within the next several years, research involving sources other than LED is nearly non-existent. Naturally, researchers are using LEDs to test theories and to develop demonstrations and products.<\/p>\n

Finally, it would be helpful if the WSJ had defined two terms \u2013 color temperature and CRI (Color Rendering Index). Both are explained in Chapter 8. Color rendering and CRI are briefly explained in this<\/a> post. CRI and color temperature are both addressed in this<\/a> post.<\/p>\n","protected":false},"excerpt":{"rendered":"

A recent article in The Wall Street Journal discussed the possibilities and benefits of lighting systems that shift color to mimic the changes in daylight. It\u2019s a complicated subject so it\u2019s not surprising that some of what\u2019s reported is inaccurate, so let me clarify a few things. First, our current understanding of how light affects … Continue reading Circadian Lighting<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[3],"tags":[27,29,30,24,59],"class_list":["post-223","post","type-post","status-publish","format-standard","hentry","category-health","tag-color-rendering","tag-color-temperature","tag-led","tag-led-color","tag-light-and-health"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p4gZSw-3B","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"jetpack-related-posts":[{"id":203,"url":"https:\/\/designinglight.com\/?p=203","url_meta":{"origin":223,"position":0},"title":"Light and Health","author":"Jason Livingston","date":"July 28, 2014","format":false,"excerpt":"The DOE has recently published a fact sheet titled Lighting for Health: LEDs in the New Age of Illumination.\u00a0\u00a0 It summarizes the Trends in Neuroscience January 2014 article Measuring and Using Light in the Melanopsin Age.\u00a0 Both publications explain the current understanding of our visual and nonvisual response to light.\u2026","rel":"","context":"In "Health"","block_context":{"text":"Health","link":"https:\/\/designinglight.com\/?cat=3"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":738,"url":"https:\/\/designinglight.com\/?p=738","url_meta":{"origin":223,"position":1},"title":"IES Disagrees With AMA on Night Time Outdoor Lighting","author":"Jason Livingston","date":"June 28, 2017","format":false,"excerpt":"Last year the AMA issued Policy H-135.927\u00a0Human and Environmental Effects of Light Emitting Diode (LED) Community Lighting, which recommended, among other things, that LED outdoor lighting should have a CCT of 3000 K or below. \u00a0The AMA made this recommendation thinking that lower correlated color temperatures contain less blue light,\u2026","rel":"","context":"In "Color"","block_context":{"text":"Color","link":"https:\/\/designinglight.com\/?cat=12"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":2910,"url":"https:\/\/designinglight.com\/?p=2910","url_meta":{"origin":223,"position":2},"title":"CCT Doesn’t Predict Circadian Impact","author":"Jason Livingston","date":"January 2, 2023","format":false,"excerpt":"Two of my IES Color Committee friends and colleagues, Tony Esposito and Kevin Houser, have just published a paper in Scientific Reports that looks at the common assumption that CCT can be used to assess circadian entrainment and other biological impacts of light. The assumption by many is that high\u2026","rel":"","context":"In "Calculations"","block_context":{"text":"Calculations","link":"https:\/\/designinglight.com\/?cat=6"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":692,"url":"https:\/\/designinglight.com\/?p=692","url_meta":{"origin":223,"position":3},"title":"LRC Responds to AMA on LEDs","author":"Jason Livingston","date":"March 27, 2017","format":false,"excerpt":"You may remember that in June of last year the American Medical Association (AMA) released a report called \u201cHuman and Environmental Effects of Light Emitting Diode (LED) Community Lighting.\u201d The report made some noise in the general press because it supported the idea that blue light from blue-pump white LEDs\u2026","rel":"","context":"In "Color"","block_context":{"text":"Color","link":"https:\/\/designinglight.com\/?cat=12"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":838,"url":"https:\/\/designinglight.com\/?p=838","url_meta":{"origin":223,"position":4},"title":"Night Shift? Not Quite.","author":"Jason Livingston","date":"May 14, 2018","format":false,"excerpt":"We've all heard about the effect blue light can have on our circadian rhythms. \u00a0It can suppress the release of melatonin, which can delay sleep and reduce sleep quality with possible long-term health consequences. \u00a0Circadian disruption has been associated with depression and increased risk of diseases such as diabetes, obesity\u2026","rel":"","context":"In "Health"","block_context":{"text":"Health","link":"https:\/\/designinglight.com\/?cat=3"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":92,"url":"https:\/\/designinglight.com\/?p=92","url_meta":{"origin":223,"position":5},"title":"The Best Light?","author":"Jason Livingston","date":"January 31, 2014","format":false,"excerpt":"In class yesterday one of my students, thinking about a project she had recently completed, asked, \"What's the best light for a hair salon?\" \u00a0I'm certain she was hoping I would tell her exactly what lamp technology and\/or lamp style to use. \u00a0Of course, it's not that simple. So the\u2026","rel":"","context":"In "Color"","block_context":{"text":"Color","link":"https:\/\/designinglight.com\/?cat=12"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"_links":{"self":[{"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/posts\/223","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/designinglight.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=223"}],"version-history":[{"count":3,"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/posts\/223\/revisions"}],"predecessor-version":[{"id":227,"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/posts\/223\/revisions\/227"}],"wp:attachment":[{"href":"https:\/\/designinglight.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=223"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/designinglight.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=223"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/designinglight.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=223"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}