Help! I can’t see my LED energy savings due to all the glare.
A UGR rating predicts how much glare your lighting solution may cause before you buy it.
If you recommend or purchase lighting solutions, chances are you’ve been hearing about glare and UGR. But did you know that WELL v2 of the WELL Building Standard, under the L04 Electric Light Glare Control category, allots points for achieving a Unified Glare Rating (UGR) of 16 or lower as a luminaire consideration, or as a space consideration, for regularly occupied spaces?
Or that the CIE (International Commission for Illumination) created the UGR formula by combining features of the Einhorn and the Hopkinson formulas while incorporating the Guth position index?
If about now you’re thinking, ‘Yikes – I wish I’d paid a bit more attention in math class,’ we’re here to help get you UGR-rating friendly.
First, some definitions. There are two types of glare: disability glare and discomfort glare. Disability glare happens when a bright light suddenly enters your field of vision, triggering an instinct to look away and momentarily reducing your visibility. It often depends upon the geographical position of the light source (relative to the individual) as well as the contrast between the source and the area surrounding it.
Discomfort glare occurs when your visibility is relentlessly reduced by excessively bright or uncontrolled light that doesn’t trigger the reaction to look away. Discomfort glare also happens when light gets ‘bounced off’ reflective surfaces, such as computer screens, whiteboards, etc. Both types of glare are subjective, and sensitivity to glare can differ greatly between individuals. And both types can be caused by direct or indirect lighting sources.
A Unified Glare Rating (UGR) indicates the amount and type of glare predicted from a lighting product or solution. Calculated on a continuum from 10 to 30, a low UGR means there will be less glare; higher UGRs predict greater glare. For example, a UGR of 10 indicates no perceptible glare, while a UGR of 30 will likely cause discomfort and/or disability glare.
UGR is derived using a precise mathematical formula: the amount of glare from a luminaire divided by the luminance of the room’s background light, while also accurately calculating the position and brightness of the referenced lighting sources.
But remember that UGR is not an attribute of a luminaire alone; it’s based on the whole lighting system application. Think of it as measuring the contrast between luminaire luminance (light brightness) and the background luminance from a specified reference vantage point.
Generally, a UGR of 16 means glare is barely perceptible, while a UGR of 19 is considered the max point for acceptable glare. And UGRs over 19 are predicted to produce glare that’s increasingly uncomfortable. In real-life application, there’s more room for variation. For example, the UGR for healthcare exam rooms should always be <19; while a higher UGR (<25) may be acceptable for high-bay applications or restaurants.
The technical UGR formula is not simple to calculate and is usually done with lighting software such as AGi32 or Dialux. Nevertheless, there are some factors that are commonly predictive of contributing to a higher UGR, including:
- Higher lumens
- Larger room sizes
- Lower ceiling heights
- Luminaire distribution with high-angle brightness
- Lower surface reflectance
- Wide spacing (generally the farther apart, the higher the UGR)
Bottom line: LED lighting systems with the highest energy efficiency are often the most likely to produce glare. This is partly true because LED lighting inherently scales down light sources to clusters of tiny points, producing the same amount of light from a much smaller footprint, which also gives people a greater impression of glare.
Fortunately, there are ways to reduce glare while maintaining the full and uniform illumination you need and the energy efficiency you want. One strategy uses special diffusers to disperse the light from each LED. Cree Lighting’s new VuePoint™ Series High-Bay does this remarkably well, and as one enthusiast described it, “tames the high power and awesomeness of LED without overwhelming the occupants in the space.”
The design of the secondary reflector system is also key. Redirecting light from the primary reflector into the secondary reflector further distributes the light, reducing more obvious glare. Other strategies to reduce glare include using narrow beam angles or positioning fixtures so they aren’t shining directly into people’s eyes. And, since glare is a relative measure, simply increasing your background luminance compared to your light sources, ceiling and wall reflectances or the amount of indirect light produced.
And if preventing the harm and hazards caused by glare aren’t incentive enough, the DLC is requiring a standard UGR table (per CIE 190-2010) for luminaires seeking DLC Premium 5.1, and for products pursuing efficacy allowances based on glare control. Our VuePoint™ Series is eligible for DLC-Premium 5.1 rebates - making it a real stand-out in high-bay environments where glare control is critical. The VuePoint’s standard lens diffuses light much more effectively than competitors so that forklift drivers and others looking upward aren’t staring into a harsh, glary light source.
But note that UGR is for indoor lighting applications only. For outdoor lighting, glare control is a whole different ball game so to speak, and a topic that we’ll continue to hear more about.
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