By WESTDEER | 30 September 2020 | 0 Comments

What is UGR?

UGR is a calculation method that helps lighting designers create schemes to avoid the discomfort of misplaced light

Unified Glare Rating (UGR) is an indicative rating for glare based on prescribed set of circumstances in a lit environment. Glare sources within a typical field of vision on the lit environment can be numerous, including daylight from windows and the internal lighting. The UGR value is calculated using a complex equation that includes the luminance value of the luminaire, the value of background luminance, the solid angle of the luminaire as seen by the viewer and several other values.


L= The luminance value of the luminaire

Lb= The value of the background luminance

ω= The solid angle of the luminaire that is seen by the viewer

p= The Guth Index. Based on the likelihood of glare, also known as Visual Comfort Probability

Σ= Shows that the equation (shown above) includes all the fittings located within the area.

The references made to UGR are held within lighting application guides such as Light Guide 7, published by The Chartered Institution of Building Services Engineers (CIBSE), which recommends that office environments do not exceed a UGR of 19. At this point it must be made clear that UGR is a function of the installation environment and not the individual luminaire. To correctly assess the level of glare a professional lighting design must be carried out. Note: UGR is not a product criteria. No product based standards apply any limits.

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