Bench Talk

LED streetlights are rapidly being deployed across the globe. They provide the advantage of long lifetimes (Mean Time to Failure: >100,000 hours), reducing the number of field replacements and the costs associated with sending out a repair crew. They also have the advantage of being more energy-efficient, producing more lumens per Watt (LPW) than alternative light sources; so that, the electric utility bills for municipalities are reduced, saving them money over the lifetime of the streetlight. Less electrical consumption means that LED lighting is better for the environment, meaning they are greener for the environment. They also can be easily modulated (turned ON or OFF) or precisely dimmed under the control of the municipality.

White LEDs used in street lighting may consist of packaged combinations of Red, Green, and Blue LEDs, but more often than not employ blue LEDs, which are built generally from indium gallium nitride (InGaN) and have a yttrium-aluminum-garnet (YAG) (Y₃Al₅O₁₂) phosphor coating placed on their emitter or emitter’s optic. This phosphor coating creates a new band of colored light by way of fluorescence and is known as phosphor light conversion. The original blue LED color mixes with the colors produced through fluorescence, and white light is produced. From the base color of blue light, white light can be realized and utilized for white LED streetlights.

But does this blue light found in LED streetlights make humans experience any negative impacts?

Well, the American Medical Association (AMA) believes so. While they do not believe that blue LEDs make people feel sad and blue, they do believe that communities should follow particular guidelines to reduce the harmful human and environmental effects of high intensity street lighting. The AMA highlights two primary points of emphasis.

First, LED street lights have a high content of blue light and create more nighttime glare for humans than traditional lighting sources. Glare may lead to safety issues, as the human eye has a hard time seeing clearly when presented with glaring light. The scattering of blue light can also potentially lead to unnecessary eye strain in humans.

Second, the AMA states that “blue-rich LED streetlights operate at a wavelength that most adversely suppresses melatonin during night. It is estimated that white LED lamps have five times greater impact on circadian sleep rhythms than conventional street lamps,” creating negative impacts for human sleep. In other words, poor lighting can throw off the human body’s biological clock and negatively impact human sleep patterns. It is not just humans that may suffer from these effects. Also other animal species can have their natural systems thrown into confusion because of biological effects produced upon them by non-natural lighting.

One way to address the issue of too much blue light is to target warmer correlated color temperature (CCT) for streetlights. This is because higher kelvin color temperatures generally mean higher inherent levels of blue light content, exactly the color of light that should be minimized at night. Historically, shifting LEDs towards warmer CCTs has resulted in lower efficacy (lumens/Watt or LPW) systems. This shift toward warmer CCTs is generally regarded as a negative for streetlight manufacturers as they wish to be able to claim the highest LPW possible.

These implications regarding negative effects upon biological agents have not gone unnoticed by the LED manufacturers. Cree, a market-leading innovator of lighting-class LEDs, LED lighting and semiconductor solutions, has responded by developing WaveMax^™ Technology, an innovative optical waveguide platform, in which its unique design works to reduce glare. The Cree^® RSW Series (Figure 1), utilizing WaveMax Technology, is the first viable LED streetlight at warm CCT (3000K, ±175K) and delivers up to 115LPW, enhanced visual comfort with reduced glare, and high color contrast leading to improved overall illumination using less energy.

Figure 1: Cree RSW^™ LED Street Luminaire, the first of a new generation of streetlights that deliver LED energy savings and reliability in a warm color temperature that is preferred in many residential applications. Image courtesy https://www.cree.com/News-and-Events/Cree-News/Press-Releases/2016/March/Cree-Reinvents-the-LED-Residential-Streetlight-with-New-RSW-Series

The AMA additionally recommends that manufacturers seek innovative ways to minimize lighting by incorporating intelligent dimming during off-peak time periods. The increased employment of various sensing technologies will likely continue to stimulate developments in this capability. Other considerations that the AMA suggests include ensuring proper light shielding of all fixtures as well as appropriate directionality in order to minimize light spill-over.

Prevent yourself from feeling blue. Ensure you work to understand the impact of light pollution and that you take the necessary steps to raise your awareness of the implications to our biological health and the environment. It could be just the panacea we all need to better enrich our lives on this planet we all call home.