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Gamma Illumination: The problem with glare

David Battersby, senior lighting designer at Gamma Illumination, explains why avoiding glare in an office lighting installation is more complicated than relying on a simple UGR19 rating.

Glare is something we all experience. Often, we compensate for it without even realising it, because it is a part of our everyday lives. Defined simply, glare is ‘a visual sensation caused by excessive and uncontrolled brightness’. That definition comes from the Lighting Research Center in New York, and we can agree with all of it except for the ‘uncontrolled’ part – because some glare is caused by very controlled light fixtures. And that’s what we’ll be discussing here.

To provide some background, there are two categories of glare:

Discomfort glare is what we experience when an overly-bright light source is within our field of vision. It may be the sun shining through a window, or the sun’s reflection off a table top, and it can be painful.

Disability glare stops us from doing what we’re trying to do. It may be the reflection of a window in a computer screen, or the approaching headlights of a car on a dark road at night. Disability glare can be very dangerous.

But generally, glare is less obvious and more insidious than that. It’s a chronic problem in an office caused by the light fixtures. And it can lead to migraines and eye problems.

As I’ve said, most of the time we deal with glare unconsciously because it’s transitory, or we can adjust our position in relation to it. But that’s not the situation in many working environments, where working positions are usually fixed in relation to surrounding light sources.

So how do we go about making sure that we can do our work properly and not suffer the debilitating effects of glare?

It’s important to note that glare is only one element that should be taken into consideration when designing a good workplace lighting scheme. Published by The Society of Light and Lighting, LG7 is a guide highlighting the importance of taking a balanced approach to lighting in order to give occupants a well-lit and comfortable working environment. It lists the factors a lighting designer needs to address to ensure the overall scheme is LG7 compliant.

 

Proflux from Gamma Illumination includes a low glare prismatic option for offices that is ideal for providing visual comfort in LG7 and BS-EN12464-1:2011 compliant schemes.

The myth of the UGR19 luminaire

There is a way of calculating the amount of glare that a lighting installation will produce. The unified glare rating (UGR) is an international index that quantifies discomfort glare. Recommended UGR figures are offered in lighting codes and help designers and engineers to ensure their designs are fit for purpose. The most common application of UGR is in the office environment, where the limiting rating is 19 – usually referred to as UGR19. This is where a particular problem has arisen.

The calculation for a UGR rating is not based solely on the photometric performance of the luminaire. UGR can only be determined by the room and workstation geometry, the height of a ceiling above a desk, and the distance of the fixtures from the viewer. It’s all about spatial arrangements. While it’s important for manufacturers to provide glare tables to indicate what a product’s glare may be in a predefined application, only the lighting designer is in a position to state that the completed installation achieves UGR19.

 

Understanding how glare works

Manufacturers who understand glare will have interpreted the way that the UGR calculations work and determined how their luminaires need to perform in an office environment. Those UGR calculations provide the information on the way the light needs to issue from a luminaire.

Luminaires that have a very bright luminous area (the ‘face’ of the fixture) may struggle to meet UGR19 because they are simply too bright. Conversely, fixtures designed as ‘dark lights’, usually with specular louvres or deep baffles, may actually be too dark to create a pleasant ambience in a room.

 

Controlling the visual environment

A good lighting scheme will be a combination of different fixtures. Some will offer good general illumination, while others provide task or localised illumination of workstations, all with the aim of creating a comfortable visual scene. It’s possible to use luminaires that wouldn’t meet UGR19 if used around a desk but would be perfect in breakout areas, meeting rooms or circulation spaces.

It’s important to remember that the working environment relates to all the spaces within a building, not just the conventional desk-based areas. This is a relatively new idea, as offices cease to be open-plan prairies of desks and are turning into multifunctional spaces that provide staff with greater freedom of movement to do their work.

 

Product selection for good office lighting

Gamma Illumination has developed luminaires specifically for the office environment, including recessed modulars and surface-mounted fixtures for open areas, feature pendants (including those with direct/indirect illumination) for localised lighting of workstations, and a comprehensive range of supporting downlights and spotlights for highlighting individual features.

Designed and manufactured at its UK head office, all Gamma products go through a rigorous in-house testing procedure. It’s this complete process that enables the company to be highly flexible, providing bespoke lighting solutions and product modifications, as well as standard products, to meet the specific requirements of designers and end users.

 

A final word on glare and product quality

A lot of the fuss that’s developed around glare has been a consequence of the LED revolution. As LEDs have got brighter, some manufacturers have chosen simply to chase the lumen output of their fixtures at the expense of the quality of illumination being provided.

The designers at Gamma understand there is a balance to be struck between lumen output, luminous efficacy and photometric performance if a good-quality visual environment is to be created.

If you’re looking for assistance in the creation of an LG7-compliant scheme, then the expertise of the lighting design team at Gamma will not only ensure compliance with the relevant standards, it will also create a visually appealing ambience with the right atmosphere that users will love.