Why is glare important?
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.
EN 12464-1:2011 is the CE standard relating to workplace lighting, focussing on two interrelated components associated with glare:
– UGR
– Luminance at 65° of <3000 cd/m2
Other relevant documentation includes SLL and CIBSE Code for Lighting.
Recommended limits for glare have been set in EN 12464-1 for a variety of workplace categories – examples below:
– UGR<16 – Technical Drawing Office
– UGR<19 – Offices, Schools
– UGR<22 – Workshops, Receptions, Retail
Factors influencing glare include:
– Source vs Background Luminance
The brighter the source is in comparison to the background light level, the greater the glare.
– Position/Direction of View
The further away the observer is from the source, the greater the glare.
– Source Size
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.
How is glare measured?
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 with reference to CIE 117:1995 and presented in a standardised UGR table.
Variables in the UGR table include:
– Wall and ceiling reflectance
– Room dimensions
– Working plane height
Achieving UGR<19 for all entries 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 UGR<19 – see ROBUS SPACE UGR 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 12464-1 (<3000 cd/m2 at 65°).
The luminance requirement in EN 12464-1 is a legacy CAT 2 Louvre requirement from LG3:1989, which was updated with the advent of anti-glare screen technology.
One obvious method of achieving UGR<19 for an LED panel for 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 in delivering its ROBUS UGR<19 LED panel ranges, although there is evidence that not all lighting companies are choosing this responsible approach.
For example, it is misleading to market and promote an LED panel as UGR<19, where it can be proven by analysing the photometric files in a lighting design that the panel achieves UGR<19 only for a maximum room size of 3.2m x 6.4m (assuming a ceiling height of 2.4m, desk height of 0.8m and that panel could be installed in either crosswise or endwise orientation).
Included here is a UGR table
produced using RELUX design software for the latest ROBUS SPACE UGR<19 panel from LED Group. UGR<19 entries in the first columns are highlighted to illustrate the glare performance at different room dimensions.
Although not a legal requirement, compliance with EN 12464-1 is recommended as best practice.
There is a real need for clarity and openness on glare requirements in the lighting market and at the very least, customers deserve to know and understand if a light fitting rated as UGR<19 does not perform as described.
In the meantime, the onus is on specifiers to look beyond claims and carry out due diligence by engaging fully with lighting companies and lighting designers in order to select products that meet the glare requirements of the project.
Mark Walshe,
Technical & Quality Manager,
Led Group & Member of the Lighting Association Ireland
References:
1. EN 12464-1:2011 – Lighting of work places. Part 1: Indoor work places
2. CIE 117:1995 – Discomfort glare in interior lighting
3. IES LM-79-08: Electrical and photometric measurements of solid-state lighting products
4. EN 13032-1:2004+A1:2012 – Measurement and presentation of photometric data of lamps and luminaires. Measurement file format.
5. EN 13032-2:2017 – Measurement and presentation of photometric data of lamps and luminaires. Presentation of data for indoor and outdoor work places.
6. EN 13032-3:2007 – Measurement and presentation of photometric data of lamps and luminaires. Presentation of data for emergency lighting of work places.
7. EN 13032-4:2015 – Measurement and presentation of photometric data of lamps and luminaires. LED lamps, modules and luminaires.
8. CIBSE SLL Code for Lighting 2012
9. CIBSE LG3
