Products + Technology
International Dark Sky Association: Blue Light at Night Threatens Animals and People
Craig DiLouie January 20, 2010
Human visual sensitivity is primarily in the green and yellow part of the spectrum and is depicted by the thin solid line. Circadian rhythms are controlled by light emitted within the dashed curve. The color of light emitted by a typical bluish-white 5500 Kelvin LED is depicted by the bold line. A large portion of light emitted by this light source falls outside of the human photopic vision range, and falls within the circadian rhythm curve. IDA recommends limiting blue light emitted below 500 nm, as indicated by the shaded section of the graph.
The rapidly expanding use of bluish-white outdoor lighting such as LED and induction/fluorescent, fueled by energy savings, presents a threat to the nocturnal environment, according to the International Dark Sky Association
According to the organization, bluish light produces high levels of light pollution with significant environmental impact. Specifically, 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. While improving outdoor lighting efficiency, bluish-white light sources escalate the environmental damage caused by artificial lighting.
IDA discourages the use of bluish-white lamp sources with a correlated color temperature above 3000K. If IDA had its way, developers of light sources should be required to refine their products to limit blue light at wavelengths shorter than 500 nm.
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My understanding is that IDA has a potential issue with blue light (defined by IDA as 500nm and shorter wavelengths) on two levels: 1) that “blue light” might cause problematic up-light situations for observatories, etc.; traditional dark sky issues, and 2) “blue light” might cause a disruption to the circadian sleep cycle, which could, in turn, cause heath and other environmental issues.
The inherent directionality of the LED light source addresses the first point in two ways: A) it makes designing a zero up-light fixture easy (you’d have to work at it to send any up-light from an LED fixture), and B) the total light output of an LED fixture can be a fraction of an HPS or Metal Halide fixture and still meet all the photometric requirements of the lighting design. So, overall, LED should have considerably less up-light, and therefore, present much less of a dark sky problem than traditional sources.
The circadian sleep cycle point is a completely specious argument. We have measured the SPD of standard cool white LED sources (6,000-10,000K), and compared them to Metal Halide (4,000K). We also compared these spectral distributions to a newer 4,000K LED product (so called, “Outdoor White”). Metal Halide lamps have much more “blue light” in their spectral distribution than any LED source – regardless of CCT — and the Outdoor White LED lamps actually have 41% less “blue light” than a comparable Metal Halide source. If “blue light” were any kind of health issue, it seems like we would have uncovered this already in the several decades that Metal Halide sources have been in broad use – indoor and outdoor – across the country and around the world.
(to download this data: http://www.drivehq.com/folder/p6772309.aspx).