Electric Magazine May/June 2018

12 ELECTRIC.IE • The Magazine & Website for the Irish Electrical Industry • Industry News Glaringly Obvious ? – UGR and EN 12464 -1 for Offices ർ As the lighting market overcomes its initial infatuation with LEDs, and starts to ask the hard questions in relation to overall light quality, glare and its standardised method of measurement, UGR (Unified Glare Rating), are increasingly important. Š› ‹• ‰Žƒ”‡ ‹’‘”–ƒ–ǫ In broad terms, uncontrolled glare increases the risk of errors, fatigue and consequently accidents, whether it be in the workplace or in the home. Glare is generally categorised as either disability or discomfort glare. We’ve all experienced the blinding effect associated with disability glare, whether it’s the poorly focussed headlights of an oncoming car on a country road at night or exiting the cinema into midday sunlight. Discomfort glare, as the term suggests, is not as drastic as disability glare, but it can take its toll if we are spending extended periods under lighting with poor glare control, which is much more common than it should be. Discomfort glare is broken down into either direct or reflected categories. ͱͲʹͶʹǦͱǣͲͰͱͱ ‹• –Š‡ •–ƒ†ƒ”† relating to workplace lighting, focussing on two interrelated …‘’‘‡–• ƒ••‘…‹ƒ–‡† ™‹–Š ‰Žƒ”‡ǣ - UGR Ǧ —‹ƒ…‡ ƒ– Ͷ͵ϓ ‘ˆ ώͳͰͰͰ…†ȀͲ Other relevant documentation includes SLL and CIBSE Code for Lighting. Recommended limits for glare have „‡‡ •‡– ‹ ͱͲʹͶʹǦͱ ˆ‘” ƒ ˜ƒ”‹‡–› ‘ˆ ™‘”’Žƒ…‡…ƒ–‡‰‘”‹‡• Ȃ ‡šƒ’Ž‡• „‡Ž‘™ǣ Ǧ ώͱͶ Ȃ ‡…Š‹…ƒŽ ”ƒ™‹‰ ˆˆ‹…‡ Ǧ ώͱ͹ Ȃ ˆˆ‹…‡•ǡ…Š‘‘Ž• Ǧ ώͲͲ Ȃ ‘”•Š‘’•ǡ ‡…‡’–‹‘•ǡ Retail ƒ…–‘”• ‹ˆŽ—‡…‹‰ ‰Žƒ”‡ ‹…Ž—†‡ǣ Ǧ ‘—”…‡ ˜• ƒ…‰”‘—† —‹ƒ…‡ The brighter the source is in comparison to the background light level, the greater the glare. Ǧ ‘•‹–‹‘Ȁ ‹”‡…–‹‘ ‘ˆ ‹‡™ The further away the observer is from the source, the greater the glare. Ǧ ‘—”…‡ ‹œ‡ The smaller the source size for a given light output, the greater the glare. LEDs are now the brightest light sources utilised in general lighting with the most light emitted per unit area. With the ongoing miniaturisation trend in the LED market, LED package sizes have reduced, while relative light output has increased; resulting in further gains in brightness and thereby leading to a greater propensity for glare. ‘™ ‹• ‰Žƒ”‡ ‡ƒ•—”‡†ǫ Glare is not solely determined by the light source, the overall room configuration must be considered. Due to the number of variables involved, with many of them unique to the specific installation site, glare cannot be distilled down to a single value for a particular light fitting. Therefore, glare is determined by carrying out photometric testing on a light fitting ™‹–Š ”‡ˆ‡”‡…‡ –‘ ͱͱͷǣͱ͹͹͵ ƒ† presented in a standardised UGR table. ƒ”‹ƒ„Ž‡• ‹ –Š‡ –ƒ„Ž‡ ‹…Ž—†‡ǣ - Wall and ceiling reflectance - Room dimensions - Working plane height …Š‹‡˜‹‰ ώͱ͹ ˆ‘” ƒŽŽ ‡–”‹‡• on the UGR table is an unrealistic expectation, as it would restrict other light source parameters and create other challenges. However, it is a reasonable expectation that all entries in the first columns of the UGR table viewed crosswise and viewed endwise would meet ώͱ͹ Ȃ •‡‡ Table. It should be noted that the UGR method does not take account of diagonal geometries, only x and y directions. The photometric measurement also facilitates the luminance (or amount of light emitted per unit area in a specific direction) of the source to be determined to ensure compliance with luminance requirements of EN ͱͲʹͶʹǦͱ ȋώͳͰͰͰ…†ȀͲ ƒ– Ͷ͵ϓȌǤ The luminance requirement in EN ͱͲʹͶʹǦͱ ‹• ƒ Ž‡‰ƒ…› Ͳ ‘—˜”‡ ”‡“—‹”‡‡– ˆ”‘ ͳǣͱ͹͸͹ǡ ™Š‹…Š was updated with the advent of anti- glare screen technology. One obvious method of achieving ώͱ͹ ˆ‘” ƒ ’ƒ‡Ž ˆ‘” example, is to restrict the beam angle. However, this could lead to a reduction in the overall illuminance uniformity on the floor, especially for lower ceiling heights. Meeting glare requirements is a delicate balancing act – good lighting design comes into its own by using the relevant light fitting photometric files with specialist light modelling software to produce designs where the competing requirements of UGR and uniformity tensors are met as per the specification. LED Group is particularly discerning ‹ †‡Ž‹˜‡”‹‰ ‹–• ώͱ͹ LED panel ranges, although there is evidence that not all lighting companies are choosing this responsible approach. GLARE LIMITATION