How to reduce light pollution caused by outdoor LED lighting?
Anyone who has flown over a city at night knows that the sight of all these lights is mesmerizing, but unfortunately, they make the sky glow and can have serious ill effects, especially on wildlife and vegetation.
As the lighting industry ditches the use of traditional light sources such as high pressure sodium or metal halide for outdoor lighting, there is an increasing focus on minimizing light pollution from outdoor LED installations.
The GFZ German Geoscience Research Center recently released the results of a study on urban street lighting in Tucson, Arizona, providing an in-depth analysis of how well-designed LED luminaires will minimize light pollution. Tucson is the city with the most LED lighting, and almost all street lights have been upgraded with wireless communication and dimming. The study was conducted over 10 days in March and April 2019, acquiring nighttime images of the Tucson region via the U.S. Suomi National Polar-orbiting Partnership (NPP) satellite. On some nights, about 14,000 of the total 19,500 street lights were set to full brightness, and other times to 30 percent bright (Figure 1).
The research team concluded that approximately 20 percent of Tucson's nighttime light comes from street lights, with the remainder generated by building signs and curtain walls, shop windows, sports fields, and more. If these conclusions are applicable to other cities, it suggests that LED lighting design may be able to solve the problem of light pollution.
To minimize light pollution or stray light, the most important tool luminaire designers use is the "BUG" rating system, where "BUG" stands for Backlight, Uplight, and Glare. The BUG rating system was developed by the Illuminating Engineering Society (IES) in conjunction with the International Dark Sky Association (IDA) to provide a unified method for evaluating the amount of stray light produced by outdoor lighting.
Stray light in outdoor environments is not only harmful, it not only causes the sky to glow, but it also causes unnecessary energy consumption. Examples of stray light are intrusive light (i.e. light coming in from an undesired location, such as from a streetlight into a nearby window), upward lit light that contributes to the glow of the sky, and glare (eye-level passing light) too much light can cause discomfort or visual disturbances).
Based on the measured lumen output in each of the three zones shown in Figure 2, a BUG rating can be obtained.
Backlight, as the name suggests, refers to the light emitted behind a lighting device. The backlight area can be further divided into four sub-areas, with corresponding emission angles ranging from 0 degrees (that is, the light points downward to the ground) to 90 degrees (most of the light points out parallel to the ground). Likewise, the glare area is also divided into four sub-areas with increasing emission angles from low glare to high glare. The upward-illuminated area consists of only two sub-areas, one containing light directed mainly upward and the other containing light directed mainly outward.
The measured lumens for each of the above divisions are referenced in the look-up table of IES TM-15-11 (Classification System for Outdoor Luminaires), and the value assigned to each parameter is in the range of 0 to 5, on which the BUG rating is based. definite. For example, a BUG class B0 U0 G0 is assigned to a lighting device that emits downward illuminating light; a BUG class B2 U0 G2 is assigned to a lighting device that emits most of the illuminating light forward and backward, but not upward. Note that the BUG rating is only one factor in determining whether a lighting fixture is suitable for a particular lighting application, generally the lower the BUG rating, the lower the chance of light pollution.