Glare is an important factor in the evaluation of lighting quality and a common problem for the high power lighting.The prevention of glare for the lighting in the stadium is particularly important. Generally speaking, glare refers to the phenomenon that the light is dazzling and making the human eye see the object unclearly, making the human eye uncomfortable, or even invisible at all. Therefore, lighting design needs to limit glare.
The standard definition of glare is:
A visual phenomenon that causes discomfort or reduces the ability to see details or objects due to an inappropriate brightness distribution or range of brightness within the field of view, or the presence of extreme brightness contrasts.
Sports lighting uses the Glare Index (GR) to assess the degree of glare, a psychological parameter that measures the subjective response to the reduced visibility and discomfort to the human eye caused by lighting equipment in outdoor sports venues and other outdoor venues.
The lighting glare index is calculated as
In the formula: Lvi is the brightness generated by the light emitted by the lamp directly directed to the eyes; Lve is the brightness caused by the irradiation site directly directed to the eyes.
After removing the constants and irrelevant terms, the above formula can be simplified：
Replace Lvi with “brightness generated by lamps”, Lve is the brightness of the venue, but the venue does not generate brightness by itself, but the brightness generated by the illumination of lamps, so replace Lve with “brightness of the illuminated venue”.
The background considered by GR is the illuminated site, that is, the working surface as the background, and other reflected lights such as wall billboards have been ignored. Different GR values indicate different degrees of glare, as shown in Table 1.
Table 1 - Glare Index and Glare Degree
The internationally recognized GR=50 is acceptable glare, so the international standard requires that the GR of sports lighting in the official competition venue is not greater than 50.
Strictly speaking, the above formula is suitable for outdoor venue lighting. My country has extended this application to indoor venues, starting from 2007. GR value of indoor venue lighting is required not to exceed 30. And major events like the Olympic Games requires that the GR of the camera is not greater than 40.
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