Published data, both on nocturnal melatonin suppression in humans and on widely accepted retinal structure and function, suggest that spectral opponency plays a role in human circadian phototransduction. We directly test subadditivity, implied by spectral opponency, in human circadian phototransduction in response to nearly monochromatic and to polychromatic light.
Adult male human subjects were exposed for 60 minutes to two intensities each of two lighting conditions, during nighttime experimental sessions. One condition consisted of light from mercury vapor lamps (450 and 1050 lx), and one condition consisted of light from these lamps filtered such that only the spectral line from this lamp at 436 nm was presented to subjects (7.5 and 15 lx).
Melatonin suppression from the filtered illumination at 436 nm alone was greater than mercury lamp illumination (containing energy at 436 nm in addition to other wavelengths), even when the sources exposed subjects' retinae to equal amounts of irradiance at 436 nm.
This direct test of subadditivity, together with evidence from neuroanatomy, supports the inference that spectral opponency is a fundamental characteristic of human circadian phototransduction.
"Because the model includes spectral opponency, responses from light stimuli created by a combination of narrowband sources cannot be predicted from the spectral sensitivity derived from narrowband light stimuli alone. In fact, for light stimuli with a particular balance of short-wavelength (e.g., around 450 nm) and long-wavelength (e.g., longer than about 510 nm) components, the response of the human circadian system to light is less than what would be predicted by an additive spectral efficiency function derived from responses to narrowband stimuli [30,31]. Emphasis for modeling was placed upon studies measuring nocturnal melatonin suppression because, in fact, there are presently no comparable spectral sensitivity functions for the circadian system using any other outcome measure (e.g., phase shifting). "
[Show abstract][Hide abstract] ABSTRACT: The present paper reflects a work in progress toward a definition of circadian light, one that should be informed by the thoughtful, century-old evolution of our present definition of light as a stimulus for the human visual system. This work in progress is based upon the functional relationship between optical radiation and its effects on nocturnal melatonin suppression, in large part because the basic data are available in the literature. Discussed here are the fundamental differences between responses by the visual and circadian systems to optical radiation. Brief reviews of photometry, colorimetry, and brightness perception are presented as a foundation for the discussion of circadian light. Finally, circadian light (CLA) and circadian stimulus (CS) calculation procedures based on a published mathematical model of human circadian phototransduction are presented with an example.
Journal of Circadian Rhythms 02/2010; 8(1):2. DOI:10.1186/1740-3391-8-2
"Following these studies based on examination with monochromatic light, it has been assumed that the containing energy of blue light in the light source dominantly affects the impact on melatonin secretion. Figueiro et al. , however, have investigated the light-induced melatonin suppression under two light conditions; one condition consisted of a mercury (Hg) vapor lamp and the other a Hg lamp fitted with a filter that allowed the passage of only blue light (around 436 nm), and found that melatonin suppression under the filtered light was greater than that with the nonfiltered light, although the light conditions had the same retinal irradiance with blue light close to the peak sensitivity of human melatonin suppression   . Meanwhile, earlier studies examining melatonin suppression under different polychromatic light sources (fluorescent lamps)    have found significant melatonin suppression under higher correlated color temperature (CCT) light compared to lower CCT light; the higher CCT light includes a larger portion of blue light than the lower CCT. "
[Show abstract][Hide abstract] ABSTRACT: In this study, 12 healthy males were exposed to various light conditions (2300K, 3000K, 5000K and dim) for 1.5h at midnight. The conditions of 3000K and 5000K were created by commercial fluorescent lamps. The light at 2300K was achieved by fitting a 3000K fluorescent lamp with a special filter that absorbed short-wavelength light. The vertical illuminance level was kept at 200lx. Saliva samples were taken before and after the light exposure. The light at 5000K suppressed melatonin secretion acutely. The 2300K lamp condition appeared to have no effect on melatonin secretion as well as the dim condition, while melatonin secretion was measurably suppressed by the light at 3000K.
[Show abstract][Hide abstract] ABSTRACT: The human brain can only accommodate a circadian rhythm that closely follows 24 hours. Thus, for a work schedule to meet the brain’s hard-wired requirement, it must employ a 24 hour-based program. However, the 6 hours on, 12 hours off (6/12) submarine watchstanding schedule creates an 18-hour “day” that Submariners must follow. Clearly, the 6/12 schedule categorically fails to meet the brain’s operational design, and no schedule other than one tuned to the brain’s 24 hour rhythm can optimize performance. Providing Submariners with a 24 hour-based watchstanding schedule—combined with effective circadian entrainment techniques using carefully-timed exposure to light—would allow crewmembers to work at the peak of their daily performance cycle and acquire more restorative sleep. In the submarine environment, where access to natural light is absent, electric lighting can play an important role in actively entraining—and closely maintaining—circadian regulation. Another area that is likely to have particular importance in the submarine environment is the potential effect of light to help restore or maintain alertness.
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