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Understanding glare to achieve UGR19
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 that 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 reflection of that sun 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 far less obvious and more insidious than that. It’s a chronic problem in an office and caused by the light fixtures. And it can lead to migraines and eye problems.
As we say above, 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.
How do we go about making sure that we can do our work properly and not suffer the debilitating effects of glare?
It is important to note here that glare is only one element of many 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 key factors that should be addressed and the importance of taking a balanced approach to lighting in order to give the occupants a well-lit and comfortable working environment. It is only by analysing these factors that a lighting designer can ensure the overall scheme is LG7 compliant.
The myth of the UGR19 luminaire
There is a way of calculating the amount of glare that a lighting installation will produce. This is called the Unified Glare Rating (UGR) and is an international index that quantifies discomfort glare. Recommended UGR figures are offered in lighting codes and help designers and engineers determine that 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 very 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; the distance of the fixtures from the viewer. It’s all about spatial arrangements. With this in mind, and whilst it is important for manufacturers to provide glare tables to indicate what a products glare may be in a predefined application, it is only the lighting designer that can accurately state that a luminaire achieves UGR19 and only after they have placed it in the scheme.
Understanding how glare works
Manufacturers who understand glare will have interpreted the way that the UGR calculations work and will have determined how their luminaires need to perform in an office environment. Those UGR calculations provide the information on the way that 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, there are those fixtures designed as ‘dark lights’, usually with specular louvres or deep baffles, that 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 fixtures will offer good general illumination, while others provide task or localised illumination of work stations, 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 break-out 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 multi-functional spaces that provide staff with a 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 work stations, 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, 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 that 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.