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Bennett, S., Alpert, M., Kubulins, V., & Hansler, R. L. (2009). Use of modified spectacles and light bulbs to block blue light at night may prevent postpartum depression. Med Hypotheses, 73(2), 251–253.
Abstract: In 2001 it was discovered that exposing the eyes to light in the blue end of the visible spectrum suppresses the production of the sleep hormone, melatonin. New mothers need to get up during the night to care for their babies. This is the time when melatonin is normally flowing. Exposing their eyes to light can cut off the flow. It may also reset their circadian (internal) clock. On subsequent nights the melatonin may not begin flowing at the normal time making it difficult to fall asleep. Over time, disruption of the circadian rhythm plus sleep deprivation may result in depression. Women suffering postpartum depression were enrolled in a small clinical trial. Some were provided with glasses and light bulbs that block blue light. Others were equipped with glasses and light bulbs that looked colored but did not block the rays causing melatonin suppression. Those with the “real glasses” recovered somewhat more quickly than those with the placebo glasses and light bulbs. The hypothesis that should be tested in large scale clinical trials is that the risk of postpartum depression can be reduced when a new mother avoids exposing her eyes to blue light when she gets up at night to care for her baby. In the meantime, all new mothers may benefit from using glasses and light bulbs that block blue light when getting up at night to care for their babies.
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Gooley, J. J., Rajaratnam, S. M. W., Brainard, G. C., Kronauer, R. E., Czeisler, C. A., & Lockley, S. W. (2010). Spectral responses of the human circadian system depend on the irradiance and duration of exposure to light. Sci Transl Med, 2(31), 31ra33.
Abstract: In humans, modulation of circadian rhythms by light is thought to be mediated primarily by melanopsin-containing retinal ganglion cells, not rods or cones. Melanopsin cells are intrinsically blue light-sensitive but also receive input from visual photoreceptors. We therefore tested in humans whether cone photoreceptors contribute to the regulation of circadian and neuroendocrine light responses. Dose-response curves for melatonin suppression and circadian phase resetting were constructed in subjects exposed to blue (460 nm) or green (555 nm) light near the onset of nocturnal melatonin secretion. At the beginning of the intervention, 555-nm light was equally effective as 460-nm light at suppressing melatonin, suggesting a significant contribution from the three-cone visual system (lambda(max) = 555 nm). During the light exposure, however, the spectral sensitivity to 555-nm light decayed exponentially relative to 460-nm light. For phase-resetting responses, the effects of exposure to low-irradiance 555-nm light were too large relative to 460-nm light to be explained solely by the activation of melanopsin. Our findings suggest that cone photoreceptors contribute substantially to nonvisual responses at the beginning of a light exposure and at low irradiances, whereas melanopsin appears to be the primary circadian photopigment in response to long-duration light exposure and at high irradiances. These results suggest that light therapy for sleep disorders and other indications might be optimized by stimulating both photoreceptor systems.
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Sasseville, A., Benhaberou-Brun, D., Fontaine, C., Charon, M. - C., & Hebert, M. (2009). Wearing blue-blockers in the morning could improve sleep of workers on a permanent night schedule: a pilot study. Chronobiol Int, 26(5), 913–925.
Abstract: Night shiftworkers often complain of disturbed sleep during the day. This could be partly caused by morning sunlight exposure during the commute home, which tends to maintain the circadian clock on a daytime rhythm. The circadian clock is most sensitive to the blue portion of the visible spectrum, so our aim was to determine if blocking short wavelengths of light below 540 nm could improve daytime sleep quality and nighttime vigilance of night shiftworkers. Eight permanent night shiftworkers (32-56 yrs of age) of Quebec City's Canada Post distribution center were evaluated during summertime, and twenty others (24-55 yrs of age) during fall and winter. Timing, efficacy, and fragmentation of daytime sleep were analyzed over four weeks by a wrist activity monitor, and subjective vigilance was additionally assessed at the end of the night shift in the fall-winter group. The first two weeks served as baseline and the remaining two as experimental weeks when workers had to wear blue-blockers glasses, either just before leaving the workplace at the end of their shift (summer group) or 2 h before the end of the night shift (fall-winter group). They all had to wear the glasses when outside during the day until 16:00 h. When wearing the glasses, workers slept, on average +/-SD, 32+/-29 and 34+/-60 more min/day, increased their sleep efficacy by 1.95+/-2.17% and 4.56+/-6.1%, and lowered their sleep fragmentation by 1.74+/-1.36% and 4.22+/-9.16% in the summer and fall-winter group, respectively. Subjective vigilance also generally improved on Fridays in the fall-winter group. Blue-blockers seem to improve daytime sleep of permanent night-shift workers.
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