What is UGR19? – The Ultimate Contractor’s Guide

UGR19 stands for Unified Glare Rating of 19 or less, which is a parameter of how bright a luminaire is in a sample room layout, and is particularly important in office spaces where workers have to spend many hours a day and would be using display terminals for a large proportion of that time.

The higher the UGR number the higher the glare from the luminaire and the increased discomfort for office workers. The glare can cause health and safety issues and welfare problems such as headaches, migraines and eyesight issues. The light fitting alone cannot be UGR19 compliant as it is not a characteristic of a luminaire but is a measure of how it performs in a physical space.

UGR19 lighting is a headache then?

Well no, UGR19 isn’t a headache but the guidelines and the working out and the procurement of it is. The UGR glare index runs from 13 to 28, luminaires with a UGR of 19 or less is the guideline for office spaces set down by the Society of Light and Lighting’s code LG07/15 Lighting Guide 07: Offices – LG7. Which in turn meet The European Standard, EN 12464-1 Light and lighting – Lighting of work places – Part 1: Indoor work places.

Specifiers are increasingly looking to meet their compliance challenges by specifying UGR19 compliant fittings with contractors. This leads to the increasingly common question “Is that fitting URG compliant?” strictly speaking the answer is No, manufacturers can only supply fittings that support the UGR19 guideline as the calculation must take into account the physical occupancy of the space that is lit.

So UGR19 is not a property of the luminaire?

That’s right it is not, So what do you do? The standard measure for a UGR<19 fitting is what the luminaire would have in a room with the dimensions of 4H/8H and degrees of reflectance of 20% for the floor, 50% for the walls and 70% for the ceiling. Most office spaces are generally not the size of a shipping container, (Unless it is an edgy office in Shoreditch and workers really are sitting in shipping containers). In real world situations, the UGR value could be lower or even higher. Proper compliance only comes when measured within the space the UGR19 luminaire is to be fitted.

UGR19 Calculation


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);
ω 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.

Don’t worry all hope is not lost with UGR19

There is a table to help. The above calculation is used to work out what the Unified Glare Rating is in rooms of different sizes, walls, ceiling and work surface reflectances. Interdistance spacing of the luminaire is centred in a grid which shows there are many different UGR ratings in different rooms.


Challenges of UGR<19 luminaires

If a luminaire is symmetrical in both directions the UGR does not change much however it is viewed. The big challenge comes when trying to source a UGR<19 compliant asymmetrical luminaire as the glare rating changes depend on whether it is viewed endwise or crosswise. There are a multitude of low glare compliant symmetrical luminaires such as low glare LED panels available on the market today, however, there are only a small handful of UGR<19 linear luminaires available at present that provide the continuous “stripe of light” visual effect desired and are reasonably priced. Many of them have a low lumen output and provide poor uniformity which means more luminaires are needed to light the space and cost are driven up.
Synergy takes great pride in listening to and supporting Contractors, Architects, Interior Designers and Lighting Engineers to meet your compliance challenges. Synergy’s clients have been asking about UGR<19 compliant LED linear luminaires and we have listened. Yes, it took us time to get it right and after 9 months of research and development, we have an exciting UGR<19 linear LED development to announce.

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