Mark S. Rea

Meeting Report: The Role of Environmental Lighting and Circadian Disruption in Cancer and Other Diseases

Light, including artificial light, has a range of effects on human physiology and behavior and can therefore alter human physiology when inappropriately timed. One example of potential light-induced disruption is the effect of light on circadian organization, including the production of several hormone rhythms. Changes in light–dark exposure (e.g., by nonday occupation or transmeridian travel) shift the timing of the circadian system such that internal rhythms can become desynchronized from both the external environment and internally with each other, impairing our ability to sleep and wake at the appropriate times and compromising physiologic and metabolic processes. Light can also have direct acute effects on neuroendocrine systems, for example, in suppressing melatonin synthesis or elevating cortisol production that may have untoward long-term consequences. For these reasons, the National Institute of Environmental Health Sciences convened a workshop of a diverse group of scientists to consider how best to conduct research on possible connections between lighting and health. According to the participants in the workshop, there are three broad areas of research effort that need to be addressed. First are the basic biophysical and molecular genetic mechanisms for phototransduction for circadian, neuroendocrine, and neurobehavioral regulation. Second are the possible physiologic consequences of disrupting these circadian regulatory processes such as on hormone production, particularly melatonin, and normal and neoplastic tissue growth dynamics. Third are effects of light-induced physiologic disruption on disease occurrence and prognosis, and how prevention and treatment could be improved by application of this knowledge.

Evaluating Light Source Efficacy under Mesopic Conditions Using Reaction Times

Rea, M. S., A. Bierman, Y. He and J. Bullough. 1995. Initial Research and Development of a New Light Source for Off-Axis Viewing at Night [report to New York State Energy Research and Development Authority]. Troy: Lighting Research Center, Rensselaer Polytechnic Institute. • Bruno, L. D. 1999. An Evaluation of High Pressure Sodium and Metal Halide Light Sources for Parking Lot Lighting [thesis]. Troy: Rensselaer Polytechnic Institute.

The Daysimeter : a device for measuring optical radiation as a stimulus for the human circadian system

Optical radiation incident on the human retina stimulates vision as well as provides time-of-day information to the brains circadian clock. The visual and circadian systems respond very differently to optical radiation. A device, the Daysimeter, was developed and tested to help progress towards a system of circadian dosimetry. The Daysimeter is a lightweight, head-mounted device that records radiation exposure estimates for both the visual and circadian systems, and is specifically designed for field use. In addition to logging spectrally weighted radiation measurements, it records head position and motion to be utilized as a representation of human circadian activity. This paper provides background on the differences between radiation for the visual and circadian systems, as well as a description of the development and testing of this prototype device.

A system of mesopic photometry

Nearly all the studies to develop mesopic luminous efficiency functions employ brightness matching. Brightness matching elicits parvocellular-channel response, which does not follow Abneys law of additivity as required by photometry. A reaction-time methodology appears to isolate magnocellular-channel response, which seems to be additive. In this study, a set of mesopic luminous efficiency functions were obtained using a novel psychophysical method, which measured reaction time differences between the two eyes. The luminous efficiency functions are well described by a simple model that linearly combines the spectral sensitivities of rods and cones. Based on this model, a preliminary system of mesopic photometry was defined and adapted for practical use.

Preliminary evidence that both blue and red light can induce alertness at night

BackgroundA variety of studies have demonstrated that retinal light exposure can increase alertness at night. It is now well accepted that the circadian system is maximally sensitive to short-wavelength (blue) light and is quite insensitive to long-wavelength (red) light. Retinal exposures to blue light at night have been recently shown to impact alertness, implicating participation by the circadian system. The present experiment was conducted to look at the impact of both blue and red light at two different levels on nocturnal alertness. Visually effective but moderate levels of red light are ineffective for stimulating the circadian system. If it were shown that a moderate level of red light impacts alertness, it would have had to occur via a pathway other than through the circadian system.MethodsFourteen subjects participated in a within-subject two-night study, where each participant was exposed to four experimental lighting conditions. Each night each subject was presented a high (40 lx at the cornea) and a low (10 lx at the cornea) diffuse light exposure condition of the same spectrum (blue, λmax = 470 nm, or red, λmax = 630 nm). The presentation order of the light levels was counterbalanced across sessions for a given subject; light spectra were counterbalanced across subjects within sessions. Prior to each lighting condition, subjects remained in the dark (< 1 lx at the cornea) for 60 minutes. Electroencephalogram (EEG) measurements, electrocardiogram (ECG), psychomotor vigilance tests (PVT), self-reports of sleepiness, and saliva samples for melatonin assays were collected at the end of each dark and light periods.ResultsExposures to red and to blue light resulted in increased beta and reduced alpha power relative to preceding dark conditions. Exposures to high, but not low, levels of red and of blue light significantly increased heart rate relative to the dark condition. Performance and sleepiness ratings were not strongly affected by the lighting conditions. Only the higher level of blue light resulted in a reduction in melatonin levels relative to the other lighting conditions.ConclusionThese results support previous findings that alertness may be mediated by the circadian system, but it does not seem to be the only light-sensitive pathway that can affect alertness at night.

Lighting the graveyard shift: The influence of a daylight-simulating skylight on the task performance and mood of night-shift workerst

This experiment was designed to establish whether lighting provided by a daylight-simulating skylight could be used to enhance the task performance and mood of night-shift workers. Subjects performed a series of cognitive tasks, gave subjective ratings of their mood and had their core temperature measured six times during each shift, for three successive nights, under the same lighting condition. Each shift ran from 00.00 hours to 07.59 hours. The subjects also kept a daily diary recording their general health, times of sleep and sleep quality for the complete period of the experiment. Four lighting conditions were experienced: a fixed low-illuminance condition; a fixed high-illuminance condition; an increasing illuminance condition simulating the changes in daylight illuminance and correlated colour temperature that occur from dawn to midday; and a decreasing illuminance condition simulating the changes in daylight illuminance and correlated colour temperature that occur from midday to dusk. There was a three day rest period before exposure to each lighting condition. The high, increasing and decreasing illuminance conditions produced higher core body temperatures and greater subjective arousal than did the low illuminance condition, on all three nights. The high- and decreasing-illuminance conditions improved the performance of complex cognitive tasks relative to the low and increasing illuminance conditions, on all three nights. There was no difference between the lighting conditions for the performance of simple cognitive tasks. The high illuminance condition led to a greater delay in going to bed following the shift than did the low-illuminance condition.

Preliminary evidence for spectral opponency in the suppression of melatonin by light in humans.

Human adult males were exposed to light from blue light emitting diodes (18 lux; 29 μW/cm2) and from clear mercury vapor lamps (450 lux; 170 μW/cm2) during night-time experimental sessions. Both conditions suppressed nocturnal melatonin concentrations in blood plasma with the blue light more effective than mercury at melatonin suppression. No additive model incorporating opsin photopigments either alone or in combination could explain the results, but a model incorporating an opponent mechanism was consistent with the present data as well as data from previously published studies.

Comparisons of three practical field devices used to measure personal light exposures and activity levels

This paper documents the spectral and spatial performance characteristics of two new versions of the Daysimeter, devices developed and calibrated by the Lighting Research Center to measure and record personal circadian light exposure and activity levels, and compares them to those of the Actiwatch Spectrum. Photometric errors from the Daysimeters and the Actiwatch Spectrum were also determined for various types of light sources. The Daysimeters had better photometric performance than the Actiwatch Spectrum. To assess differences associated with measuring light and activity levels at different locations on the body, older adults wore four Daysimeters and an Actiwatch Spectrum for seven consecutive days. Wearing the Daysimeter or Actiwatch Spectrum on the wrist compromises accurate light measurements relative to locating a calibrated photosensor at the plane of the cornea.

Simulated driving performance and peripheral detection at mesopic and low photopic light levels

This paper describes research conducted to measure peoples ability to perform a simulated driving task and respond to peripheral targets at mesopic and low photopic light levels under different spectral power distributions (SPDS). A computer-controlled driving simulator apparatus was employed. An achromatic projected driving scene could be controlled in terms of luminance and SPD using filters. Subjects drove simulated roadway courses; their average speed, frequency of crashing and subjective ratings of brightness were measured. As expected, driving performance and subjective ratings improved with photopic luminance. SPD had no measurable an driving performance or brightness ratings. Subsequent tests shawed, however, that the detection of targets located in the peripheral visual field (positioned where potential visual hazards to a driver might be located) was highly dependent on both luminance and SID. Rods and cones both appear to contribute to peripheral target detection even at luminances traditionally considered to be strictly photopic. The results and their implications are discussed in the context of previous research.

Retinal mechanisms determine the subadditive response to polychromatic light by the human circadian system

Light is the major synchronizer of circadian rhythms to the 24-h solar day. The intrinsically photosensitive retinal ganglion cells (ipRGCs) play a central role in circadian regulation but cones also provide, albeit indirectly, input to these cells. In humans, spectrally opponent blue versus yellow (b-y) bipolar cells lying distal to the ganglion cell layer were hypothesized to provide direct input to the ipRGCs and therefore, the circadian system should exhibit subadditivity to some types of polychromatic light. Ten subjects participated in a within-subjects 3-night protocol. Three experimental conditions were employed that provided the same total irradiance at both eyes: (1) one unit of blue light (lambda(max)=450 nm, 0.077 W/m(2)) to the left eye plus one unit of green light (lambda(max)=525 nm, 0.211 W/m(2)) to the right eye, (2) one unit of blue light to the right eye plus one unit of green light to the left eye, and (3) 1/2 unit of blue light plus 1/2 unit of green light to both eyes. The first two conditions did not differ significantly in melatonin suppression while the third condition had significantly less melatonin suppression than conditions 1 and 2. Furthermore, the magnitudes of suppression were well predicted by a previously published model of circadian phototransduction incorporating spectral opponency. As was previously demonstrated, these results show that the human circadian system exhibits a subadditive response to certain polychromatic light spectra. This study demonstrates for the first time that subadditivity is due to spectrally opponent (color) retinal neurons.