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“Glare” is to light as “noise” is to sound – CIE Research Roadmap on Glare

30 Jun 2019

The luminaire on the top (a) has a diffuser over the LEDs so it has a larger surface area. The one on the bottom (b) has individual visible LEDs. Both of these luminaires would exhibit glare undercounted by the UGR formula because UGR would use the full luminaire aperture as the luminaire size, not just the size of the diffusers or the sum total area of the LEDs (Photos courtesy Pacific Northwest National Laboratory, Richland, WA, USA)

Above: The luminaire on the top (a) has a diffuser over the LEDs so it has a larger surface area. The one on the bottom (b) has individual visible LEDs. Both of these luminaires would exhibit glare undercounted by the UGR formula because UGR would use the full luminaire aperture as the luminaire size, not just the size of the diffusers or the sum total area of the LEDs (Photos courtesy Pacific Northwest National Laboratory, Richland, WA, USA)

 

Glare has always been a relevant topic, especially since electric light levels began to increase. With high intensity light sources like LEDs, the problem culminated in the last few years. CIE addresses this topic in its recent publication CIE 205:2013: Review of Lighting Quality Measures for Interior Lighting with LED Lighting Systems. Furthermore the Joint Technical Committee JTC 7 is still working on this topic. A short overview on the topic and CIE's activities is presented.

Excessive light intensity, regardless of the source type, can have several unwanted effects on people. The presence of bright sources in the periphery of the field of view may cause a reduction in visibility or cause feelings of discomfort. The discomfort might be associated with the bright peripheral light sources detracting the eye from the intended gaze direction, although the exact mechanism causing this discomfort is not fully understood. Another effect occurs when the field of view itself is experienced as too bright or dazzling, typically in daylight conditions that require sunglasses.

Glare has been under study for over a century, but it really took off in the 1940s when increasing electric light levels gave rise to complaints about discomfort caused by excessive light. As a result, a multitude of glare formulae were proposed, each formula being based on a limited set of experimental results on a specific light source (gas discharge lamps, fluorescent tubes, daylight through windows, etc) in a specific application (office lighting, street lighting, sports lighting, etc).

Disability caused by glare has been successfully attributed to light scattering in the eye. The scattered light of bright sources creates a veiling luminance on the retina, which reduces the contrast of the retinal image. As a result, this glare effect could be well defined and tested experimentally. The prediction formula for disability glare, as described in CIE 146:2002 CIE equations for disability glare, is therefore widely accepted and applied without reference to a specific application.

 

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