Compared with conventional lighting, the blue-rich white LED street lighting is five times more disruptive to sleep cycle.

Excessive blue light emitted by light emitting diodes (LEDs) can adversely impact human health, says a report released recently by the American Medical Association (AMA) Council on Science and Public Health, reaffirming the long-suspected impact on human health.  The report looked at LED street lighting on U.S. roadways, where nearly 10 per cent of street lighting is from LEDs.

While the LED lighting has several advantages — up to 50 per cent reduction in energy consumption, increased visual effectiveness, longer lamp life of 15 to 20 years or 50,000 hours, absence of mercury or lead, and decreased overall costs — the excessive blue light emitted by LED lighting can adversely impact health and environment.

The human eyes perceive the large amount of blue light emitted by some LEDs as white colour. The blue light directly affects sleep by suppressing the production of melatonin hormone which mediates the sleep-wake cycle in humans. Compared with conventional street lighting, the blue-rich white LED street lighting is five times more disruptive to sleep cycle, the report says.

Although more research is needed, available evidence suggests a long-term increase in the risk for cancer, diabetes, cardiovascular disease and obesity caused by chronic sleep disruption caused by blue light.

The excessive blue wavelength contributes to glare effects as a result of more scattering in the human eye.  Contrary to popular notion that bright LED lighting increases road safety, the report says that discomfort and disability glare caused by unshielded, bright LED lighting negatively impacts visual acuity thus “decreasing safety and creating road hazard”. Glare forms a veil of luminance that reduces the contrast and thus reduces the visibility of a target. It also notes that unshielded LEDs lighting causes papillary constriction, leading to “worse night-time vision between lighting fixtures.” Intense blue spectrum can even damage the retina.

The correlated colour temperature (CCT) of first-generation LEDs, which are currently used, is 4,000 Kelvin. Higher CCT values indicate a greater amount of blue light is emitted, and in the case of 4,000 K LED lighting, 29 per cent of the spectrum is emitted as blue light.

But at 3,000 K, the blue light emitted is only 21 per cent and appears “slightly warmer in tone”.  While discomfort and disability glare is reduced, there is only a 3 per cent drop in energy efficiency compared with 4,000 Kelvin LED lighting.

More attention should be paid on proper design, shielding and installation so that no light shines above 80 degrees from the horizontal, the report says. According to June 10 study (World atlas of artificial night sky brightness) published in the journal Science Advances, unless blue-light emission from 4,000 Kelvin LED street lighting is restricted, retrofits using these lamps could result in 2.5 times increase in lighting pollution.

“Strong consideration should be made for effective shielding and limiting CCT of outdoor lighting to 3,000 Kelvin or lower,” the AMA recommends.  Some countries have already taken steps to address the problem. Hawaii uses filter to block the blue wavelength and Quebec uses amber LEDs.

On the environmental front, unshielded light on beaches is said to have caused a massive drop in turtle populations as hatchlings disoriented by electric light are unable to reach the water safely. Upstream migration of fish, such as salmon returning to spawn, is disrupted from “too blue bridge lighting,” the report says. In fact, a brightly lit bridge in Washington State is shut off during salmon spawning season.

Published in The Hindu on June 23, 2016