Health effects from lighting cover a very broad range, from the physio-biological effects of radiation to the effects of pollution associated with lighting. Topics discussed here are:
The most significant health issue associated with lighting relates to the identification at the turn of the century of the non-visual photoreceptors known as intrinsically-photosensitive Retinal Ganglion Cells (ipRGCs) and the corresponding photo-pigment nicknamed "melanopsin". These photoreceptors do not provide stimulus to our visual system but instead provide information to the systems that control our day/night (a.k.a. circadian) cycle of waking and sleeping. This is achieved by suppressing the hormone melatonin, which occurs when the ipRGCs are sufficiently stimulated by electro-magnetic radiation. Perhaps the most important aspect of this new sensory system is that it is most responsive to short-wave optical radiation (SWOR), more than to light as it is technically defined. Indeed, the ipRGCs and corresponding melatonin suppression/production system operate with a radiation-sensitivity-function that has its peak sensitivity around 464 nm - which strongly corresponds to the radiation that comes from "blue sky", as well as the visible radiation produced by TVs, computer screens and most "white" LEDs. For humans the effects from SWOR echo those from sugar, caffiene or cocaine - such as elevated blood-pressure, elevated body-temperature, elevated pulse rate, even anxiety, sleeep disorders and reduced levels of melatonin in the blood. Long-term these responses increase the probability of developing "diseases of civilization" such as obesity, diabetes, hypertension and cancer. The link with cancer has a particular quirk: the "messenger" hormone melatonin is recognized as a significant anti-oxidant, "cancer-fighting" (oncostatic) compound. This means that the presence of melatonin tends to reduce the start and growth of cancers. Since melatonin in humans can be suppressed by exposure to SWOR, from whatever source and at whatever time of day, this is clearly a significant issue that deserves greater attention and more research.
Application of this information also offers opportunities. One particular opportunity has been siezed by the folks at f.lux, who offer software that adjusts computer displays automatically over the course of the day, reducing the "blue light" (SWOR) during nightime hours at that location. They have also developed a webpage with research information and a discussion board. The research they cite is consistent with what is presented here, and also extends beyond it.
Seasonal affective disorder (SAD) is a condition that has been treated using light exposure in suitable spectra, intensity and duration, e.g. 10,000 lx from "daylight" fluorescent lamps for an hour, to change mood and physical health. Similar treatment has been recommended for recovering from "jet-lag" through the "resetting of the diurnal cycle" that is associated with the hormone melatonin and responds to exposure to SWOR or high levels of light. Similar treatments has been shown to be effective for helping people with conditions such as Alzheimers, by reducing restlessness at night and promoting wakefulness during the day.
Such circadian-cycle control through exposure to optical radiation is found in life-forms ranging from humans to algae, and the introduction of such radiation at night has been identified as light pollution resulting in loss of habitat for different species. These effects are magnified by the fact that the SWOR that impacts bio-clocks is also the radiation most reflected by the atmosphere, so the impacts can extend beyond the horizon of the initial light source(s). This form of pollution associated with lighting is skyglow, the uplight that is reflected by the atmosphere back to the ground. Such atmospheric reflection is very dependent on the spectral power distribution of the radiation. The relative effects from different sources can be estimated by the Rayleigh Scatter Index (RSI). Since other life forms' diurnal cycle may be sensitive to radiation in the same way we are, the interaction of atmospheric scattering and melanopsin may be important. A summary of the RSI evaluation of sources - including "melanoptic" sensitivity - is here. This is a growing problem due to increasing exterior light pollution, particularly from "blue-rich" sources such as metal halide and typical "white LEDs".
A separate health issue is the pollution from generation of electricity, part of the effects from lighting. Mercury is a compound that is released into the environment, principally from coal-fueled power plants, that becomes methyl-mercury, a potent neurotoxin that "bio-accumulates" meaning it is passed up the food chain. Mercury is also present in every metal halide and fluorescent lamp (and some HPS lamps), which may be hazardous waste and should be disposed or recycled accordingly.
Metal halide lamps have in the past been associated with "non-passive end-of-life" which is another way of saying they can explode, which is a health hazard. An associated hazard is the potential for eye or skin damage from direct exposure to ultraviolet radiation from metal halide lamps that have broken or missing glass envelopes.
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