Journal
JOURNAL OF BIOLOGICAL RHYTHMS
Volume 34, Issue 2, Pages 195-204Publisher
SAGE PUBLICATIONS INC
DOI: 10.1177/0748730419830013
Keywords
light at night; circadian; melatonin suppression; spectrum; cyan-gap lighting; cyan-deficient lighting
Categories
Funding
- LumiLeds
- Light and Health Alliance (Acuity Brands)
- Light and Health Alliance (CREE)
- Light and Health Alliance (Current Powered by GE)
- Light and Health Alliance (Ketra)
- Light and Health Alliance (Osram)
- Light and Health Alliance (Philips)
- Light and Health Alliance (USAI Lighting)
- NIH Training Program in Alzheimer's Disease Clinical and Translational Research [NIA 5T32AG057464]
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The intrinsically photosensitive retinal ganglion cells are the main conduit of the light signal emanating from the retina to the biological clock located in the suprachiasmatic nuclei of the hypothalamus. Lighting manufacturers are developing white light sources that are devoid of wavelengths around 480 nm (cyan gap) to reduce their impact on the circadian system. The present study was designed to investigate whether exposure to a cyan-gap, 3000 K white light source, spectrally tuned to reduce radiant power between 475 and 495 nm (reducing stimulation of the melanopsin-containing photoreceptor), would suppress melatonin less than a conventional 3000 K light source. The study's 2 phases employed a within-subjects experimental design involving the same 16 adult participants. In Phase 1, participants were exposed for 1 h to 3 experimental conditions over the course of 3 consecutive weeks: 1) dim light control (<5 lux at the eyes); 2) 800 lux at the eyes of a 3000 K light source; and 3) 800 lux at the eyes of a 3000 K, cyan-gap modified (3000 K mod) light source. The same protocol was repeated in Phase 2, but light levels were reduced to 400 lux at the eyes. As hypothesized, there were significant main effects of light level (F-1,F-12 = 9.1, p < 0.05, eta(2)(p) = 0.43) and exposure duration (F-1,F-12 = 47.7, p < 0.05, eta(2)(p) = 0.80) but there was no significant main effect of spectrum (F-1,F-12 = 0.16, p > 0.05, eta(2)(p) = 0.01). There were no significant interactions with spectrum. Contrary to our model predictions, our results showed that short-term exposures (<= 1 h) to cyan-gap light sources suppressed melatonin similarly to conventional light sources of the same CCT and photopic illuminance at the eyes.
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