Glare:
Glare will be evaluated by two criteria: (1) discomfort glare and (b) disability glare.
a. Discomfort Glare
The discomfort from glare is described by a Glare Control Mark, GM, which expresses on an ordinal scale the subjective appraisal of the degree of discomfort experienced. The value of GM is associated to different glare sensations as follows:
GM-1 "Unbearable"
GM-2 "Disturbing"
GM-5 "Just admissible"
GM-7 "Satisfactory restriction"
GM-9 "Unnoticeable"
b.Disability Glare
The method for evaluation of disability glare is based on the Holladay formula. According to the formula, the effect of glare is quantified by an equivalent uniform luminance, which describes the effect of the stray light in the eye: lowering the contrast. The relative threshold increment, TI, is expressed as the difference between the threshold under glare condition and its value without glare, expressed in percent of the value without glare.
The veiling luminance, Lv, represents the illumination at the eye due to glare sources and is the equivalent uniform luminance, in footlamberts, superimposed over the entire visual field.
The recommendations concerning the restriction of glare in road lighting installations have been given in terms of GM and T1. These values should be considered as minimum requirements. If higher values for G and lower values for TI are economically feasible, preference should be given to such an improvement of the glare restrictions.
Glare will be evaluated by two criteria: (1) discomfort glare and (b) disability glare.
a. Discomfort Glare
The discomfort from glare is described by a Glare Control Mark, GM, which expresses on an ordinal scale the subjective appraisal of the degree of discomfort experienced. The value of GM is associated to different glare sensations as follows:
GM-1 "Unbearable"
GM-2 "Disturbing"
GM-5 "Just admissible"
GM-7 "Satisfactory restriction"
GM-9 "Unnoticeable"
b.Disability Glare
The method for evaluation of disability glare is based on the Holladay formula. According to the formula, the effect of glare is quantified by an equivalent uniform luminance, which describes the effect of the stray light in the eye: lowering the contrast. The relative threshold increment, TI, is expressed as the difference between the threshold under glare condition and its value without glare, expressed in percent of the value without glare.
The veiling luminance, Lv, represents the illumination at the eye due to glare sources and is the equivalent uniform luminance, in footlamberts, superimposed over the entire visual field.
The recommendations concerning the restriction of glare in road lighting installations have been given in terms of GM and T1. These values should be considered as minimum requirements. If higher values for G and lower values for TI are economically feasible, preference should be given to such an improvement of the glare restrictions.
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