According to EN 12464-1 the level of direct glare from luminaires of a lighting system has to be determined by the table of the CIE – Unified Glare Rating – method (UGR).
- 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 light in the direction of the observer's eye.
- ω Solid angle in steradian (sr) of the light-emitting surface of each light relative to the observer's eye.
- p Postionsindex by Guth for each lamp, depending on their spatial deviation from the main line of sight.
The UGR values are in the range of 10 ("no glare") and 30 ("unacceptable discomfort glare") graded: 13, 16, 19, 22,25, 28. The larger the UGR value, the greater the probability of glare. These limits are assigned to specific activities and spaces, and must not be exceeded.
The change of the UGR value for different observer positions can be determined with the help of advanced UGR table or by the formula. If the maximum UGR value exceeds the UGR limits in a room information about the appropriate arrangement of workplaces should be made.
For luminaires with direct light a UGR table is automatically generated. You can find these in the luminaire data sheet of the output. Their required SHR (Spacing to Height Ratio) of 0.25 or 1 you can set in the standard control (File - Preferences - standards).
For a more detailed analysis, you can place UGR calculation points or UGR calculation areas in the mode “calculation objects”.
In the tool calculation objects you can select the number of viewpoints on the step size and the range of viewing angles.
After the calculation, you can check the results in the results tool. The required values from the space profile are used for comparison. The room profile can be selected in the assesment zones tool according to the design specifications.
Note that the values in calculation points and surfaces with the UGR formula be determined because the exact observer position and orientation of these are well known. According to EN 12464-1 this is allowed. However, too few studies are available to confirm the applicability of the limits of this method. The limits for these technologies are still under discussion.
In the outputs you can find a results overview for the calculation areas and points. The graphic shows the position of the calculation objects.
You can also find a schematic representation for UGR calculation areas, where is clearly displayed in the location, direction, and the calculated values.
The white circle shows the considered view directions, the gray area the non-considered area. Each line in the graph represents a line of sight. If the UGR value for a viewing direction is above the specified limit, the value is displayed with a red line.
Values below 10 are not shown, values above 30 with shortened, roan lines.The maximum UGR value for each site can be found at the center of the diagram.
The recommended by the standard grading of the values 10, 13, 16, 19, 22, 25 and 28 are displayed as a scale in the diagram.