Wednesday, September 14, 2011

Does LED lighting at night have bad effects?

  John Wallace
  Senior Editor
  Laser Focus World
Scientists have been talking for many years about how artificial lighting can cause poor sleep. To that, you might say, "So shut the lights off." But the scientists are talking about the disruption of our circadian (day/night) rhythm, which would last beyond the time the bedside lamp was turned off. Here are just a couple of news snippets about the effects of burning the midnight oil.

Melatonin suppression
A team of researchers from Israel, Italy, and the U.S. are now saying that the light emitted by a white-light LED suppresses melatonin in humans at a relatively high rate. Melatonin suppression is apparently not a good thing, causing "behavior disruptions and health problems," as noted by a University of Haifa press release on the study. This is because it disrupts the circadian rhythm.

The researchers compared three types of bulbs: white LEDs, metal-halide lamps (used in car headlights and outdoor lighting), and high-pressure sodium (HPS) lamps. Melatonin suppression is caused by blue light; HPS lamps, with their orange-yellow hue, were the controls in the experiment. The results showed that metal-halide lamps suppress melatonin at a rate more than three times greater than the HPS bulbs, while white LEDs suppress melatonin at a rate more than five times higher than the HPS bulb. The study, titled "Limiting the impact of light pollution on human health, environment and stellar visibility," was recently published in the Journal of Environmental Management.

But research the easy way doesn't work
Another study, recently conducted by the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute (Troy, NY) found that satellite images of outdoor lighting are unrelated to actual light levels reaching the eye--which challenges previous studies linking areas on satellite images of bright outdoor lighting with increased incidences of breast cancer.

"After shift work was identified as a probable carcinogen by the World Health Organization, some studies were published that claimed a statistical association between light at night and the incidence of breast cancer. However, these studies relied on satellite photometry and subjects' self-reports of bedroom brightness as measures of light exposure. None of these studies employed actual light measurements at the eye," said LRC Director and principal investigator Mark Rea. "Before statistical associations between light at night and disease can graduate to a cause and effect relationship, it is necessary to measure the light as a potential causal agent." This apparently can't be done from space.

"It is important to note, however, that these findings do not undermine the foundational data using animal models that link melatonin suppression by light at night and cancer risks, nor does it contradict the statistical association between shift work and breast cancer risk in humans," add d Rea.

Dark sky at night, retiree's delight
A couple of years ago, a group called the International Dark-Sky Association (IDA; Tucson, AZ) issued a statement noting that "the rapidly expanding use of bluish-white outdoor lighting threatens visibility at night and jeopardizes the nocturnal environment worldwide." The statement specifically referred to LED-based outdoor lighting.

The IDA defines blue light as any light with a wavelength shorter than 500 nm, and says that lamps emitting blue light increase glare and compromise human vision, especially in the aging eye. "Short-wavelength light also increases sky glow disproportionately," states the IDA. "In addition, blue light has a greater tendency to affect living organisms through disruption of their biological processes that rely upon natural cycles of daylight and darkness, such as the circadian rhythm."

Rayleigh scattering, which occurs much more strongly at short wavelengths, is a hindrance to astronomers. Apparently, it's the bane of old people too.

What, me worry?
I believe in safety (seat belts were kind of a nice invention, I think). But I also suspect that a cup of evening coffee has a far greater impact on sleep than whether a nearby light bulb is a warm or a cool white. I believe that the increased energy efficiency of LEDs will be of great benefit in many ways. So, please join me in giving a boost to the beleaguered LED light bulb -- switch to decaf.

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