UGR or Unified Glare Rating is a measurement of Glare. It is a complex measurement and varies from 10 (minimum glare) to 30 (maximum glare). Below 10, it is regarded as insignificant.
It is dependent on the brightness of the Luminaire, but also on the brightness of the background and other factors. Because of this, the location of the Viewer is relevant. Because of these Factors the UGR is not solely related to the Luminaire, but to a specific installation. For example, a 200w LED Streetlight left switched on may cause glare at night time but cause no glare during day time. Standing above the lights or behind the lights might cause no glare, but a Viewer standing in the middle of the road mayexperience glare.
If a manufacturer shows a UGR of say 19 (which is often the recommended limit for office lighting), this would indicate they have made assumptions about the Room where it will be installed – probably a 50% wall reflectance and a 70% ceiling reflectance. A rating limit of 22 – 28 may apply for different types of interior Industrial areas. Lighting Standards give guidelines for Glare in different applications.
VeeLite uses advanced lighting software which calculates the UGR for each area.
The attached link to Dialux website has a general explanation on UGR.