Those involved in LED lighting design and applications might want to pay attention to research on the effects of darkness on living organisms.
Scotobiology is the label given to a field of study encompassing the need of biological organisms for darkness -- specifically, for alternating periods of light and dark.
Mankind has been using artificial light at night (the scotobiologists abbreviate it as ALAN) for perhaps 200,000 years. Until less than 150 years ago, our light sources were based on fire. In the incandescent era (until a few decades ago), artificial light was based mostly on blackbody radiation, e.g., radiation from a hot tungsten filament. Fluorescent, sodium, and LED lighting have spectral characteristics diverging considerably from their blackbody cousin. The elevated blue components of the spectra are of particular concern for those researching darkness adaptation and melatonin production.
Beyond dark skies
Light pollution at night has been a growing problem since early in the 20th century. Most people, if they are aware of light pollution at all, have heard of it in the context of preserving dark skies -- for the sake of astronomers, but also just because humans love looking up at the stars and planets at night. But scotobiologists are attempting to broaden the conversation to encompass the effects of ALAN on the health and well-being of humans and other creatures -- from animals to plants to bacteria.
There is plenty of research on these effects going back to the 1920s. A 2009 study looked across 164 countries and found elevated levels of prostate cancer in men with the most exposure to ALAN. A decade earlier, a major study of female nurses found higher breast cancer risk for those who worked more night shifts. Melatonin disruption caused by fluorescent light is believed to be a factor.
The disruptions of ALAN affect more than just the human population. In introducing their 2006 book Ecological Consequences of Artificial Outdoor Lighting, editors Catherine Rich and Travis Longcore wrote: "From nest choice and breeding success of birds to behavioral and physiological changes in salamanders, many organisms are seriously affected by human alterations in natural patterns of light and dark."
Correcting the mistakes of the past
Robert Dick, one of the founders of the Canadian Scotobiology Group, told me in an email: "LEDs are an opportunity to improve the state of lighting across the planet -- but only if we correct the mistakes of the past. Presently, we are reaffirming these errors." Dick has developed and patented a scotobiology-compliant luminaire that provides not only lower light levels, energy savings, and full cutoff, but also a reduced-blue spectral distribution that should cause less disruption to living things at night.
Dick, who is also an active participant in the Royal Astronomical Society of Canada's dark-skies initiatives, describes some of the science and engineering behind the luminaire in this presentation from last year. It's hosted on the website of an astronomy center at one of Canada's Dark-Sky Preserves.
As you work with light, are you giving any thought to the biological need for darkness?
— Keith Dawson , Editor-in-Chief, All LED Lighting