Bright lights, another headache?

Glare is a wonderful thing; it creates sparkle, glints and artistic flare. On the other hand glare is an awful thing; creating difficulty to see, veiling detail and tiring the eye.

Whether you love it or not depends on the situation, a club compared to the office, relaxing in the sun compared to driving the car. But we have developed measures to try and quantify glare and what the limits should be. UGR, or the unified glare rating, has been around for a long time. No, it’s not perfect. For one thing, how often do you sit, head at 1.2m above the floor, half way along a wall in a rectangular space and look directly across the room. In sports, outdoor, we use GR and you could ask how often a competitor looks along a playing area at precisely 2 degrees below the horizontal.

Many will shout that our glare measures are at best poor and that you should ignore it. I disagree, at least in part. UGR and GR are not ideal, but they do have a basis in science and at least give an indication of the glare sensation.

No we don’t often experience glare in the way the calculation defines it, but we have to start somewhere.

A good designer will already know how their lighting will impact a space and the people within it. Glare and sparkle will be carefully balanced to create an ambience just right for the task, whether it is reading, communication or simply enjoying a fine glass of Rioja.

Others amongst you will claim that glare measures certainly don’t apply with LED… seems no established measure quite suit this new technology. And actually, at first look I would agree. Not because there is anything more wrong about the calculation. In fact it’s pretty technology independent. The issue comes from experience. LED fittings simply seem to be glarier. I don’t mean those that use large format, professionally diffused optics, but those with small lensed sources.

There does seem to be a relationship between the spacing of the LED, the number of LED in a fitting and our point of view. No doubt Arnold Wilkins would also add that spatial discomfort theory (1/spatial-frequency) is at work, but UGR is not at fault.

Inside the calculation you have to look at the luminance and the size of its projected area. Traditionally it has been possible to sum this across a large fitting as the light source also was pretty large. But LED changes that. A number of small intense sources, evenly spaced, are not the same as one summed area. Perhaps we should stop blaming UGR and start thinking about good optical design? Perhaps we should look at each source as its actual intensity and size and start weeding out poor lenses, uncontrolled and extreme intensity; perhaps we should apply the UGR calculation as if a fitting with multiple sources is in fact a series of individual luminaires?

I’m sat under a fitting with 64 LED and I can’t see any individual light source. It features really great optical design and indeed was specified by a lighting designer who works with me and knew what they were doing. The glare sensation is, in my view, better than the fluorescent equivalent. The UGR certainly is no worse.

Whilst you might like your sparkle if you are suffering glare, don’t blame LED. Don’t blame, or ignore the UGR method. Try blaming the optical designer and the designer you allowed to specify your lighting. Great design, even with LED, doesn’t come free.

By maclighter

A Chartered Engineer in Lighting, though trained in mechanical, with 30 years lighting design, technical, manufacture and marketing experience. A trusted mentor, designer, emergency and DIALux trainer, speaker and past president of the Society of Light and Lighting. Get in touch if I can help you out.