"Light is beneficial, but dark is also beneficial," says Prof. Abraham Haim, head of the Center for Interdisciplinary Chronobiological Research at the University of Haifa. "We should live in darkness at night, but since early human evolution one of the properties humans wanted to change was the darkness. So we need to ask what type of illumination is less harmful."

 

That was the goal of the study, recently published in the Journal of Environmental Management by Haim and other researchers using data from astronomers, physicists and biologists at the Light Pollution Science and Technology Institute in Italy and the National Geophysical Data Center in Boulder, Colorado. Haim joined the team about a year ago.

 

The scientists investigated the effect of different types of outdoor lighting on light pollution and melatonin, in order to suggest practical steps for balancing productivity, energy expenditure and public health.

 

 

 

White LED light (which is actually blue light on the spectrum) is emitted at short wavelengths of between 440-500 nanometers. The study showed that this type of light suppresses the body's production of melatonin five times more than the orange-yellow light given off by traditional high-pressure sodium (HPS) bulbs. Metal halide bulbs, often used for stadium lighting, suppress melatonin at a rate more than three times greater than the HPS bulb.

 

That's a problem, because melatonin, which is made in the pineal gland at night, is essential for biological rhythms and also has anti-oxidant and anti-cancerous properties. At the same time, the brighter light causes light pollution - obscuring the stars and disrupting ecosystems. One of the study's authors, Pierantonio Cinzano, is a world light pollution expert. However, LED is favored more and more because it doesn't get as hot as HPS bulbs and therefore cuts energy consumption.

 

The researchers make some concrete suggestions that could alter the situation without throwing our world into total darkness. For example, lampposts could be adjusted so that their light is not directed beyond the horizon, which would significantly reduce light pollution. Most importantly, they suggest what might be considered obvious: White light should be limited to times and circumstances where it is absolutely necessary.

 

"We illuminate our world too much," says Haim, who admires how Italy dims its lights at night. "To save energy, let's put the lights off when we leave the room. We don't have to use lighted billboards overnight, and we don't have to light up roads that are not used heavily at night."

 

Haim isn't optimistic that any of the recommendations will be adopted, due to all sorts of economic and political realities in a modern nation. But he still wants to get out the message that "if we would work only from 550 [nanometers] and higher, suppression of melatonin would be less."

In sleep studies done by one of his graduate students at the University of Haifa, and also in Switzerland, people exposed to short-wavelength LED lighting for two hours in the early evening did not experience the normal nighttime reduction in alertness or body temperature, and their melatonin levels did not increase as they should have. "When we used the same duration of exposure and the same intensity from incandescent wavelengths of 550 or more, they did not get these effects," he says. 

 

Ideally, Haim concludes, bulb manufacturers should be required to disclose what wavelengths are produced by each bulb and how that might affect melatonin production and light pollution. "Short wavelengths should be eliminated from the nocturnal spectrum," he says.