Unified Glare Rating Overview

The calculation of the Unified Glare Rating (UGR) value is based on the CIE 117-1995 standard (discomfort glare in interior lighting). It allows you to evaluate the visual discomfort by comparing light sources' luminance over the general background luminance.

Calculation formula

The UGR calculation formula is:



  • Lb is the background luminance (cd/m²);

  • L is the luminance of the luminous parts of each luminaire in the direction of the observer’s eye (cd/m²);

  • w is the solid angle of the luminous parts of each luminaire at the observer’s eye (steradian);

  • p is the Guth position index for each individual luminaire which relates to its displacement from the line of sight.

UGR value ranges

UGR values generally range from 10 to 30:

  • From 0 to 10: glare is insignificant

  • From 10 to 22: glare is acceptable

  • From 22 to 28: glare is uncomfortable

  • Superior to 28: glare is intolerable

Refer to UGR Calculation chapter to see how to calculate UGR in the Virtual Human Vision or the Virtual Photometric Labs.

Principle

The Unified Glare Rating principle is to add up all luminaires' luminance and compare this value over the background luminance. An observer's eye will be more easily dazzled by a light if the background luminance is low.

The solid angle and the Guth position index are corrective factors allowing to consider the fact that the observer's eye is not supposed to look directly at light sources but will rather look in front of him, on what is called a workplane.



Refer to UGR Tables chapter to see how to generate an HTML report containing detailed results and simulation parameters of your room configurations.