Why does ‘glare factor’ matter?

This question has been answered by the technical team at Ansell Lighting.

Glare that is caused by a light fixture is described as either ‘discomfort’ or ‘disability’ glare. It means that someone working at a task either finds it difficult to see what they are doing, or impossible to see what they are doing. These days, a common cause of glare is a luminaire mounted in the ceiling in front of someone’s workstation.

We tend to think that glare is all about people working at computers, but it can be a problem for anyone who needs to focus on a task, be it an industrial process or an activity in the retail and leisure sectors. A bright light that stops you working is a problem.

Glare values have become an issue since modular LED panels became the luminaire of choice for commercial spaces. As these fixtures have increased in brightness, so their glare component has risen. Lighting designers need to ensure that luminaires are appropriate to purpose and location.

The lighting industry has addressed the issue of acceptable brightness by creating the unified glare rating (UGR). It’s a mathematical way of determining the ‘brightness’ of a luminaire in a given setting. And at first sight it’s a daunting equation. Without going into detail, these are the important factors:

  • The luminance value of the luminaire, as reported by the photometric data
  • The value of the background luminance, based on standard values for different surfaces
  • The viewing angle from viewer to luminaire, measured from the horizontal
  • A mysterious factor called the Guth Index, which is based on ‘visual comfort probability’

The important information to take away from this is that the UGR is based on a luminaire fitted within a space – it’s not just a luminaire in a box. A luminaire may be labelled as being ‘UGR19 compliant’, but that can only be taken as meaning that, in all likelihood, once the luminaire parameters are put into the UGR formula, that fixture will be compliant.

The UK health and safety regulations require that lighting at work should be suitable and sufficient; ‘suitable and sufficient’ is referenced back to the lighting design criteria developed by the Society of Light and Lighting (SLL). So UGR compliance is essentially a legal requirement. So this stuff is important.







Comments 2

LEDs are here to stay. Get some blue-light blocking sun glasses. The whole world is not going to accommodate you unfortunately.

I regret to give this you input, but I have no choice. The reality is there that blue white and bright white LED lights are having a terrible impact on migraine sufferers. I am having my independence removed from me by bright white/blue white LED lights that are being installed everywhere. They create pain on such a severe level I am forced to say indoors because of LED street lighting. I never had to do this before. I cannot use pedestrian crossings because of the pain caused by LED lights of both overhanging streetlights and the increasing use of LED car headlights. I am not an older person. I consider myself a fit person who used to pound the streets for miles of long distance running....until the local council installed LED lights. I am being denied the right to my own free will as a consumer and customer, because the pain from LED lights in supermarkets and LED lights in supermarket freezers cause me severe agony in my eyes and a guaranteed follow up migraine and cluster pain. I am becoming isolated in the community: I cannot enter sports centres, clinics, dentists, pharmacies, hospitals, community centres, colleges, help centres; all because of the pain in my eyes and migraine, caused 100% from the LED lights that are now popping up everywhere. It is agony. I am also effectively being rubbished as a useful employee, because of the pain and distraction I get from LED: my future is a very bleak one. LED lights, namely the bright white and blue/white LED have created a disability for me when before I did not have a disability before whatsoever. I am horrified at the UK wide failure to consider that the blue part of the light spectrum (of which LED emits a great deal of) is a trigger for many migraine suffers who are affected by strong light. I never had this degree of suffering before, nor this degree of disability. The bright white and blue white LED lights have stopped my life dead. They need an anti-glare filter at the very least. We need the copper tone/yellow versions, or versions which do not use the agonising and distracting blue part of the light spectrum. Human health and quality of life is going downhill from this type of LED. The reality is there. I am living evidence of this. Please do not ignore it.

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