According to EN 12464-1, the level of direct glare caused by luminaires in a lighting installation is to be determined according to the table method of the CIE - Unified Glare Rating - method (UGR). The method is based on the formula:
- Lb background luminance in cd/m², calculated from Eind/π with Eind as vertical indirect illumination at the observer's eye.
- L average luminance in cd/m2 of the light emitting surface of each luminaire in the direction of the observer's eye.
- ω solid angle in steradiant (sr) of the light emitting surface of each luminaire relative to the observer's eye.
- p postion index by Guth for each luminaire, depending on their spatial deviation from the main line of sight.
The UGR values are graded in the range of 10 ("no glare") and 30 ("unacceptable psychological glare"): 13, 16, 19, 22, 25, 28. The greater the UGR value, the greater the probability of glare. These limit values are assigned to specific activities and rooms. They must not be exceeded.
The change in the UGR value for different observer positions can be determined with the help of the extended UGR table or by means of the formula. If the largest UGR value in a room exceeds the UGR limit value, information should be provided on the appropriate arrangement of workplaces.
A UGR table is automatically generated for luminaires with direct light components. You can find this in the product data sheet of the documentation. You can set the required SHR (Spacing to Height Ratio) of 0.25 or 1 in the settings for standards (File – Settings – Standards).
For a more detailed analysis, you can place UGR calculation points or UGR calculation surfaces in the "Calculation objects" mode.
You select the number of viewing directions to be checked in the "Calculation objects" tool via the step size and the viewing angle range.
After the calculation, you can check the results in the "Results overview". The target values from the room profile are used for comparison. The room profile can be selected in the "Spaces" tool according to the planning specifications.
Note that the values on calculation points and surfaces are determined with the UGR formula, as the exact observer position and viewing direction are known for them. According to EN 12464-1, this is permissible. However, too few studies are available to confirm the applicability of the limit values for these procedures. The limit values for these procedures are still under discussion.
You will find a result overview of the calculation surfaces and points in the documentation. The graphic shows the position of the calculation objects.
In addition, for UGR calculation surfaces you will also find a schematic representation in which the location, direction and the calculated values are clearly shown.
The white partial circle shows the directions of view taken into account, the blue area shows the area not taken into account. Each line in the diagram represents a direction of sight. If the UGR value for a viewing direction is above the specified limit value, the value is shown with a red line.
Values below 10 are not shown, values above 30 are shown with shortened, dashed lines. The maximum UGR value for the respective location is found in the centre of the diagram.
The gradation of the values 10, 13, 16, 19, 22, 25 and 28 recommended by the standard are shown as a scale within the diagram.