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Concern about glare could be preventing specifiers and other users from choosing LEDs for certain applications. The problem of glare is one of design, however, not the result of an inherent weakness in LEDs themselves. Properly designed LED bulbs can produce a uniformly bright and pleasing light that is all but indistinguishable from popular but less efficient halogen bulbs.
The potential for glare from any light source increases with greater lumen output and smaller source size, so as manufacturers strive for higher light output from smaller LED sources, the potential for glare to occur increases.
To compound the problem, market pressures to reduce LED costs have led some manufacturers to hit target lumens by using fewer, higher-output LEDs, which also increases the potential for glare. One of the ways that manufacturers can control glare is by using good quality, appropriate optics. Good optical management is key to providing comfortable, useable, glare-free light from LEDs.
Exterior lighting for pedestrian pathways, and commercial/institutional interior lighting where linear fluorescent lamps have been in use, are two areas where special care needs to be taken in adopting LED lighting. Interestingly enough, these locations and applications can experience glare regardless of the light source being used. However, inappropriate LED lighting can make already present glare an even bigger distraction than before.
Recent research, consumer input, and experiences have shown that the BUG (Backlight, Uplight, and Glare) ratings developed for outdoor lighting measurement may not be what we need to rate pedestrian-scale exterior lighting systems’ suitability for use. A Department of Energy GATEWAY study of walkway, street and path lighting on a college campus and in a residential community found that the lamp elevation angles used when calculating BUG ratings are not satisfactory for predicting glare perception in pedestrians in these locations.
With interior applications such as high bay lighting, downlighting and residential lighting, well known glare rating systems like the Visual Comfort Probability (VCP) and the Uniform Glare Rating (UGR) can be unreliable. They may have worked well for older lamp types, but for the common luminaires and systems of today they are left wanting, according to the Department of Energy.
Specifiers and end-users who choose LED lamps and luminaires based only on rated data may be surprised to find that their new LED system produces more glare than indicated by the numbers.
LED is having a tough time taking the place of linear fluorescent lamps because of the efficacy and lifetime of the incumbent technology although this is changing as LED T8 tube replacements begin to come of age. Adoption of LEDs can be further hurt by increased glare potential. Linear fluorescent lamps are relatively large, diffuse light sources that are often used in locations which can be very sensitive to glare concerns. In some locations, even the switch from old T8 to newer T5 fluorescent lamps created glare issues because of the smaller surface area of the tubes, so it is no wonder that LED can be difficult to implement in some situations.
A recent Department of Energy Caliper study of troffer lighting found that troffers with odd or distracting patterns, or noticeable bright patches on lenses, were found to be more glaring than those with softer gradients, while LED lamps that use mixing chambers, remote phosphors, and diffusing media in front of emitters help to reduce the potential for glare.
But again, because there is no widely accepted glare metric for these sources and applications, there is no quick or easy way for specifiers and users to determine a product’s potential for glare in a given situation. They are instead left to depend on costly and time-consuming mockups to evaluate the glare in a given situation.
Glare is eliminated when the LED bulb distributes light evenly, maximizing the emitting area and redistributing the ultra bright points. This redistribution, which produces uniform brightness over a wide area, requires careful lens design. While many manufacturers use diffusers to reduce the intense points of light, diffusers can reduce overall light output. Reflectors, meanwhile, are a proven way to control light distribution while preserving intensity. Leapfrog, where anti-glare technology has been a top priority in our PAR lamps, uses patented lens redistribution technology and reflectors in combination.
Leapfrog’s “intelligent optics” solution is one example of an LED technology that matches the incumbent technology for light intensity without producing higher luminance and glare.