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Sunday, December 8, 2019

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Blue light in LEDs
Sam Manafi
/ Categories: Uncategorized

Blue light in LEDs

A few weeks ago the American Medical Association (AMA) adopted community guidance on street lighting that caused an stir in the lighting community. Several lighting experts have commented on the AMA's findings and have provided their perspectives. According to a statement release on the AMA web site on June 14, 2016 AMA adopted this guidance as a way to "strengthen the AMA's policy stand against light pollution and public awareness of the adverse health and environmental effects of pervasive nighttime lighting". While the essence of the guidance constitutes a well-intended and fair policy, it focuses only on minimizing blue light content leaving other practical elements of the issue out of the discussion. For example, isn't it just as important to minimize light output, and design for appropriate levels of lighting / dimming relevant to time of night, type of location, height and distance of poles, density of population and wildlife, etc. Clearly, customization is critical when it comes to street and neighborhood lighting. As always it comes to good judgment by practitioners in the field to develop lighting solutions that fit well with the specifics of the application.

As Bruce Kinzey, MSSLC Director of Pacific Northwest National Laboratory has stated in an article in the most recent issue of The Light Post, it is the spectral content of a light source that is the key factor of melanopic content contributing to glare and circadian sleep rhythms. Therefore, lowering the emission of blue light  is only part of the solution. For example, the melanopic content of 4000K or 5000K LEDs may be higher versus High Pressure Sodium (HPS) bulbs, but almost in every case the lumen output of a comparable LED light source is lower than HPS contributing to a similar overall melanopic content level. Therefore it is possible to use a higher CCT with lower lumen output and still lower the effects of glare.

It is important to note that the negative environmental impact of LEDs are substantially lower than HPS and HID lights. Consider the many attributes of LEDs (controllability, superior distribution, higher lumen / W) that make LEDs superior to any other type of light source available today.

The takeaway here is that the reduction of blue light is a good advice when combined with lowering the lumen output and matching the specifics of an application with the appropriate light source. This approach creates the needed balance to maximize performance and minimize cost. Given the attributes of LEDs, and with careful planning required efficiencies and performance for street lighting can be achieved.

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