http://www.archlighting.com/technology/blue-light-hazard-and-leds-fact-or-fiction_o
Blue-Light Hazard and LEDs: Fact or Fiction?
The advent of solid-state lighting in everyday applications has renewed research interest in whether its spectral profile can lead to increased health risks.
...Typical white LEDs consist of gallium nitride (GaN) and blue dye and a phosphor coating that converts a portion of the blue light into white. These phosphor-coated white LEDs can be fabricated with customized spectral profiles, but the process necessitates a spike in blue radiant energy. The phosphors produce a second, broader, and, in some cases, higher peak between 550 and 650 nanometers.
LEDs with correlated color temperatures (CCTs) topping 3000K are often singled out for their high blue content. In June, for example, the American Medical Association released a report cautioning against the use of high-CCT LEDs in outdoor applications, citing health concerns such as melatonin suppression and circadian disruption—which are technically distinct from blue-light hazard. Although CCT does correlate with a source’s blue-light content, the U.S. Department of Energy (DOE) states in its 2013 “Optical Safety of LEDs” fact sheet that the proportion of blue emissions in the spectrum “is not significantly higher for LEDs than it is for any other light source at the same CCT.”
The brightness of LEDs has also raised concerns. As a point source, the diodes emit a concentrated directional light that can be unpleasant to view directly. Still, their output is less than what the DOE cites as a risk for blue-light hazard: a luminance exceeding 4 gigacandela per square meter, and an illuminance exceeding 400,000 lux. Moreover, in interior lighting applications, the sources are often diffused, mitigating any discomfort...
...Considerable research has focused on the impact of short-wavelength light on the eye’s functions unrelated to vision, such as melatonin and circadian regulation. Although light exposure in general can inhibit the release of melatonin, the hormone that signals to the body the onset of darkness or night, studies have shown that blue light seems to exert a more powerful effect. For example, boosting light levels and color temperature for 30 to 45 minutes has helped astronauts feel more awake, says Stan Walerczyk, principal of San Francisco–based Lighting Wizards, an energy-efficiency consultancy.
Other evidence suggests that nocturnal use of LED-lit mobile devices and computer displays, which emit a bluish cast, can delay sleep. Walerczyk recommends avoiding “blue light one to two hours before you go to bed.” For those who can’t stay away from their screens, free apps such as F.lux will increase and decrease the blue component in an electronic display according to the time of day, he says. Apple also offers a “night shift” option in its mobile devices that casts a hue atop screens during evening hours.
In outdoor applications, such as street lighting, LEDs with higher amounts of blue light could potentially suppress melatonin production, as the June AMA report alleges. However, the DOE and the LRC, in their responses to the AMA report, note that any conclusions to be drawn need to factor in the amount and duration of light exposure...
LED Streetlights Are Giving Neighborhoods the Blues
Early adopters of LED street lighting are struggling with glare and light pollution
...Lately, lighting companies have introduced LED streetlights with a warmer-hued output, and municipalities have begun to adopt them. Some communities, too, are using smart lighting controls to minimize light pollution. They are welcome changes, but they’re happening none too soon: An estimated 10 percent of all outdoor lighting [PDF] in the United States was switched over to an earlier generation of LEDs, which included those problematic blue-rich varieties, at a potential cost of billions of dollars.
The episode invites a few questions: How did an energy-saving technology that looked so promising wind up irritating so many people? Why has it taken so long for the impacts of blue-rich lighting to become widely known? And why did blue-rich LEDs so captivate municipal lighting engineers long before better options reached the market?...
When I was very young the streetlights in our backward town were bulbs on a reflector that emitted a yellow light.
the next lights were blue sort of florescent sealed lights
Then the abominable pink ones
Now the white ones that are so grim.
Blue light isn’t the best for skin complextions. Amber is. It makes almost anyone appear more attractive. Blue light, in that regard, is a bit harsh, as would be most other colored lighting.