UGR16: what’s going on?

A year ago, manufacturers were complaining about the rigours of UGR19. Specifiers – or, more to the point, facilities managers – had woken up to their responsibilities to provide lighting conditions that worked in favour of office staff. A new generation of LED panels was threatening to flood offices with horribly glaring light caused by an excessive light output -so bringing UGR19 out of the cupboard was the best tool available to bring a modicum of control to the situation.

Now here’s a reminder, if we need it: THERE IS NO SUCH THING as a UGR-anything luminaire. The Unified Glare Ratio (UGR) is calculated in a less-than-handy equation. It requires a set of inputs that ask as much about the space within which the luminaire is to be fitted than the luminaire itself.

  • L is the luminance value of the luminaire.
  • Lb  represents the value of the background luminance.
  • ω is the solid angle of the luminaire as seen by the viewer.
  • P is The Guth Index. It’s a factor based on the line-of-sight relationship between viewer and luminaire.

Having fun?


The thing that we can see immediately from this equation is that the UGR number will get bigger as the physical size of the luminaire and/or its lumen output increases; For any given situation, the background luminance will be assumed, as will the Guth Index, so they are effectively constants in any comparative equations. Its the luminaire that matters.

So how did we arrive at a situation where Unified Glare Ratings of 17 – 16 – 13(!) are on offer? Let me offer a suggestion; I think it took just three steps to get here.

iGuzzini: Laser Blade

First, we have to go back to Frankfurt Licht+Bild, 2016 where iGuzzini launched the Laser Blade, a fantastic range of discreet downlights, built up of small single-cell LED modules with a specular reflector. It was the most original use of the ‘darklight’ reflector since ERCO introduced its range of cone downlights back in the day. The Laser Blade took the architectural design community by storm and awards rained down upon the company.

XAL: Unico

Then, two years later at Licht+Bild, XAL showed us their Unico range. Was Unico inspired by Laser Blade? It used the same basic optical technology, but the brave (sensible?) decision to build a range out of a low-glare LED module that was four-times bigger than the Laser Blade meant that the range could be expanded to include a greater variety of light distribution. That made a kind of sense for Unico to be considered as an option for general illumination, putting some distance between it and iGuzzini’s dramatic high-contrast Laser Blade. Once again, awards were lavished on the Belgian company by a grateful lighting community.

And so, to today. As we all know, it doesn’t take long for the lighting industry to pick up on trends – and here we go again. There are copies of the Laser Blade out there, but it will always be a bit of a niche product (electricians don’t like making small square holes in ceiling, for one thing).

Unico, on the other hand, has gone viral; or, at least, the Unico style has gone viral, which means that single cell LEDs are being fitted inside highly specular reflectors everywhere that you look. And now the marketeers (those guys again!) have to make a market for them.

Spinal Tap offered us the volume control that went up to 11; the LED did the opposite and set up a never-ending race for smaller numbers. As LED efficacies increased, power figures got smaller – and as glare becomes a thing for end-users to worry about, what’s better than a glare rating that’s lower than anything we currently need. Small is beautiful; right?

“These go to 11”

Can we be clear on this? There is NO NEED for anything less than UGR19 for office lighting. The idea is to have a lighting installation that is comfortable to those working beneath it, but we still want light to be distributed widely around the volume. That’s quite important.

Lower UGR numbers inevitably describe a narrow-beam downlight. We never expected the original generation of tungsten halogen downlights to function as general illuminators (but, please,  let’s not get into this argument!) – so a row, or a square, of single-cell LED modules doing the same thing is not necessarily a good idea.

And if we want another comparison, let’s never forget the horrors of the cat1 interior (welcome to the batcave, my friends). We’ve been trying to pull away from the old cat1/cat2 style of interior for years, so let’s not go back there just because someone thought it was a good idea to make a low-brightness LED cell.

Oh, and I’d like to think that luminaires are designed first and outputs confirmed afterwards. I’m beginning to think that, in this case, we’re seeing the cells built first and the inappropriate photometric data being justified as a consequence.

Just a thought.

Because we’re really trying to get away from things like this.

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