Glare index

Glare index

A value for predicting the presence of glare as a result of daylight entering an area. The glare index is affected by the size and relative position of fenestration, orientation to the sun, sky luminance, and interior luminance. The glare index is similar to the index of sensation and the discomfort glare rating, which are used for electric-lighting applications.
References in periodicals archive ?
Several studies evaluated the relationship between shading controls, glare problems, and energy usages (Wienold 2007; Chan and Tzempelikos 2013; Tzempelikos and Shen 2013) while others used the glare index as an indicator to control shading devices (Oh, Lee et al.
We obtained values of daylight glare index (DGI) from luminance maps by means of high dynamic range images (HDRI) [Inanici and Galvin 2004].
Those kinds of experiments are the source behind many well-known glare indexes. The same strategy was used in the present study: the use of an emulated window in a laboratory to investigate glare not just as a visual stressor but also as a cognitive one.
The glare metrics included are: the Hopkinson Daylight Glare Index ([DGI.sub.7x], [DGI.sub.2000]) (Hopkinson, 1962), recommended by the International Energy Agency (IEA) Solar Heating and Cooling (SHC) Program Task 21 daylighting performance monitoring procedures (IEA, 2000); the Unified Glare Rating (UGR) recommended by the ASHRAE performance Measurement protocols (pMp) for commercial buildings (ASHRAE, 2011); the CIE glare index (CGI), recommended by (Einhorn, 1969); and interior global vertical illuminance (IllumintVert), recommended by Osterhaus (1998).
Average luminances of large window areas using shielded sensors have commonly been used to compute the daylight glare index (DGI) [IEA SHC Task 21, 2000] as well as numerous other discomfort glare indices.
The Illuminating Engineering Society of North America (IESNA) recommended contrast ratio limits and Hopkinson Cornell Large Source Glare Index (DGI) (1) are used as a basis for evaluation.
The Hopkinson-Cornell large-source glare index (daylight glare index or DGI) is a metric commonly used to evaluate discomfort glare for large-area sources of glare such as windows [Hopkinson and Bradley, 1960; IES 1962].
To address this problem, a weighted daylight glare index ([DGI.sub.w]) sensitive to infrequent periods of perceptible-to-uncomfortable glare was implemented [Carmody 2004].
On the other hand, visual performance studies (Blackwell, 1959; Boyce, 1973; Rea and Ouelette, 1991) and visual comfort metrics such as Daylight Glare Index (DGI) (Hopkinson, 1972; Chauvel and others, 1982) and Daylight Glare Probability (DGP) (Wienold and Christoffersen, 2006) establish a relationship between luminance, comfort, and visibility.
In the 1950s the IES Glare Index System was developed to reduce the possibility of visual discomfort through over-bright luminaires when seen in the normal field of view (FOV).