Everything You Need To Know About Unified Glare Rating

We’ve all, at some point in our professional careers, been forced to work at a computer where the glare on the screen is nothing short of a nightmare.

Glare occurs when the presence of bright light sources, luminaires or windows.

Uncomfortable glare is quantified by the Unified Glare Rating (UGR).

Previously, glare calculations were complex and involved totaling all the light from all sources at a particular angle entering the eye at a particular location.

The UGR simplifies this by providing a rating for a luminaire which enables us to determine if it is likely to cause discomfort in specific types of work situation.


“UGR = 8 log [0.25/Lb Æ©(L2ω/p2)]

L represents the luminance value of the luminaire

Lb is the value of the background luminance

Ω is the solid angle of the luminaire as seen by the viewer.

p is The Guth Index. This is a factor based on the likelihood of glare, known as Visual Comfort Probability.

The Sigma sign (Æ©) means that the equation includes ALL fittings within a space.

As you can see from the values used in the equation, a UGR calculation can only be realistic when applied to a physical space. It cannot be measured in a test room.

What this means is that it is impossible for a manufacturer to claim that it is UGR19 compliant as this depends entirely on the workspace and the tasks being undertaken.

Size Matters

In offices used for normal (clerical) type work, the LUX level will be around 500 and, at this lighting intensity, a UGR of 19 is specified as the maximum glare rating above which discomfort may occur.

Because glare is subjective to so many factors including positioning of workspaces and relative positioning of lighting, a small office is unlikely to have noticeable glare even if the luminaires are above the UGR19 guideline.

This will not be so in a larger workspace where distant luminaires could easily cause discomfort in the working sight line or by reflectance from a computer screen.

What this shows us is that choosing the right lighting is the most important part of making sure your workplace is properly lit.

Using the right luminaires for the work space you have is the best way to ensure that your staff are comfortable when working at a computer.

Take a look at our wide range of products to find the best lighting solution for your needs.  


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