UGR stands for unified glare index. It’s a numerical way of defining how bright a luminaire appears in-situ and it goes back to the earliest editions of lighting codes for interior lighting – office lighting, in particular.

In the early days of desk-top computers there was a serious problem caused by the reflections of light fittings in highly-reflective screens. This is the best-known image and was included in all editions of the lighting codes:

Of course, it didn’t take long for the screen manufacturers to make the whole issue redundant by shifting to low-reflective screens. And that, we thought, was that.

The unforeseen legacy of this was the ubiquitous Cat 2 fluorescent luminaire. Although lighting standards for offices ran to several dozen pages everyone, from specifier to manufacturer to supplier to installer, boiled all that advice and wisdom down to a single abbreviation, and Cat 2 was born.

Effectively, it meant that office lighting should be provided by luminaires with a 65deg angle cut-off. The crass use of Cat 2 as the defining feature of interior lighting so annoyed the Society of Light and Lighting (SLL) that the ‘Category’ system was abandoned in 2002 as a direct consequence of this misuse.

Let’s write that date again . . . 2002. We’ve since had two lighting codes for office environments, Lighting Guide 3 and more recently Light Guide 7.

Compliance with those codes requires a full analysis of illuminances, reflectivity, task geometries, so as to arrive at any kind of meaningful specification. But despite the changes in design requirements, and a lot of SLL foot-stamping, suppliers and installers still looked for a convenient shorthand. And finally, Cat 2 can be forgotten because we have a new one to play with: welcome UGR19.

Let’s be clear from the outset. Nothing has changed here; we’re still in a world defined by Sun headline writers. There is no such thing as a ‘UGR19-compliant’ luminaire. There are luminaires that function in such a way that they support a UGR-compliant scheme but compliance can only be proven once the ergonomic metrics of how the luminaires relate to occupancy in a real space have been established.

UGR Calculations can be made using the Relux Software, It is possible to achieve UGR19 Compliance with a standard Opal Panel if the area is small enough as your eyeline tends to be looking at the wall opposite this is why manufacturers use the term UGR19 *  this star tends to mean small offices only

IF in doubt what to use ask the Mastertrade Lighting Design Team to run a quick Relux Scheme. If you don't have the time for this stay with UGR19 Tpa Panels