Unified Glare Rating
What is UGR value and when is it required and used?
The abbreviation UGR stands for »unified glare rating«. The UGR value is a dimensionless parameter which provides information about the degree of psychological glare of a lighting installation in an indoor space. UGR values are defined in steps within a scale of 10 to 30. So UGR 19, for example, means that 65% of observers »did not really feel disturbed« by the glare. Conversely, of course, this also means that the remaining 35% felt disturbed by the glare.
“The lower the UGR value, the less direct glare is experienced by the observers.”
The following example taken from a real-life situation demonstrates clearly the influence which the ratio of these brightness levels to each other can have on the glare effect:
Imagine that you are driving along a road at night with no street lighting. A car now comes towards you with headlights on full beam. You are blinded by the strong light and are hardly able to keep your eyes on the road. Imagine the same situation on a sunny summer’s day. The same vehicle approaches again with the headlights on full beam. Now you are far less likely to be blind ed by the headlights. Yet the properties of the headlights have not changed at all. The degree of direct glare results here mainly from the contrast to the surroundings (i.e. the background illuminance)
The UGR Calculation
Prior to installation a lighting scheme designer would use sophisticated software such as Relux or Dialux to calculate the lighting requirements for every room, i.e. quantity of luminaries and mounting positions. Luminaire manufacturers provide electronic files which the software uses to perform the necessary calculations. It is not enough to simply kno w the lumen output of a luminaire, to be able predict how it will behave in a given installation. Differences in the dimensions of the room, mounting height, surface reflectance’s, room usage etc. will all influence the final UGR value. A professional lighting design will give a true assessment of a luminaires ability to satisfy the requirements of a potential installation, and highlight any problems well before a single fitting has been purchased and installed.
Low UGR Panel
If we were to examine the interior of a typical good quality LED panel we would find three main components behind the diffuser:
- The LED strips that generate the light
- A ‘Light Guide Board’ that takes the light and directs it towards the diffuser
- A reflective sheet that forces stray light within the panel back towards the Light Guide Board
Though a tried and tested construction method it can result in a very wide beam angle, i.e. 120°, and in certain installations this can lead to higher UGR levels than BSEN 12464: 2002 specifies. However, a recent innovation in diffuser design has resulted in an effective solution to the problem. UGR has been developed with market leading nano structure technology that minimizes glare and refocuses the light towards the object of illumination. By refocusing the light down, less light is spilled, therefore minimizing glare spills from the sides. In addition to minimizing glare the nano structure technology also ensures only the required amount of light is used, consequently saving on energy that would have otherwise been wasted from light spill.