Understanding UGR: What is UGR and How to Read UGR Tables
We often receive inquiries from customers about UGR. The most frequently asked questions are: what is UGR and how should we read the data in UGR tables? Below, we will explain some relevant knowledge about UGR, including how to obtain UGR values and the relationship between UGR and glare.
1. What is UGR?
Glare mainly includes disability glare and discomfort glare. Disability glare is glare that reduces visual performance and visibility. It is mainly caused by stray light from high-brightness light sources in the field of view entering the eye and scattering within the eyeball, causing a decrease in the clarity and contrast of images on the retina. Discomfort glare refers to glare that causes visual discomfort but does not reduce visibility.
Both types of glare are evaluated using UGR (Unified Glare Rating), which is one of the main contents in lighting quality evaluation in lighting design. UGR value is an important indicator for measuring the degree of glare, which is crucial for indoor lighting design.
The glare levels corresponding to UGR values are shown in the following table:
Figure: UGR values and corresponding glare levels comparison table, used to evaluate glare levels in lighting environments
2. How to Obtain UGR Tables for Luminaires? How to Get UGR Values?
How to obtain UGR values is a concern for many customers. Obtaining UGR tables requires professional testing equipment and methods. First, after measuring the luminous intensity distribution data of luminaires using YIMING Technology goniophotometer, UGR tables can be obtained through the calculation methods introduced in CIE117-1995 and CIE190-2010. YIMING Technology goniophotometer is a professional equipment for measuring the luminous intensity distribution of luminaires. By measuring luminous intensity distribution data at different angles, UGR values can be calculated. As shown in the figures below.
Figure: CIE 117-1995 UGR table, calculated based on luminous intensity distribution data measured by YIMING Technology goniophotometer
Figure: CIE190-2010 UGR table, showing the standard calculation method for how to obtain UGR values
3. How to Read UGR Table Data?
How to understand the data in UGR tables? Which data should we select to provide to customers?
UGR tables are glare evaluation tables given under specified luminaire arrangements, room sizes, room ceiling, wall, and work surface reflectance coefficients, and human eye observation positions. The reflectance coefficients of ceiling, walls, and work surfaces in the table are relatively easy to understand, so we won't elaborate here. Regarding room dimensions, some friends may not fully understand. The room size here is defined as a ratio to the height from the human eye to the luminaire. If the height from the human eye to the luminaire H=2m, then X=2H, Y=4H, the X direction of the room is 2*2=4m, and the Y direction is 4*2=8m. These parameters are very important for accurately calculating UGR values and evaluating glare levels.
Figure: UGR table data explanation, showing detailed parameters for how to obtain UGR values after YIMING Technology goniophotometer testing
As shown in the green box in the figure above, it is important to note the explanation below the numbers in the UGR table, because some software provides data in the table that has not been corrected for luminous flux. If this is not noticed, the provided data will have significant deviations. In Hangzhou YIMING Technology's GMS series luminaire luminous intensity distribution testing software, there is an option button for whether to correct, as shown in the blue box in the figure below. By default, luminous flux correction is selected, so you need to pay attention to this setting when printing reports for customers. Correct correction settings are crucial for obtaining accurate UGR values.
Figure: Luminous flux correction option, an important setting when testing luminous intensity distribution with YIMING Technology goniophotometer and calculating UGR values
4. How to Use UGR Table Data?
With so much data in the UGR table, how should we use it? Or when customers ask what the UGR of our luminaire is, which value should we give them? Before CIE 190:2010 was published, CIE117-1995 was always used to evaluate discomfort glare of indoor luminaires. CIE117 requires selecting and calculating UGR values based on your room size, room conditions, and luminaire installation spacing. After CIE190-2010 was published, standard conditions were given, simplifying the calculation significantly. In DLC SSL Technical Requirement V5.1, it is clearly stated that the UGR value reported is the corrected UGR value under the following conditions: X=4H, Y=8H, S/H=1, reflectance of 70/50/20. As shown in the figure above, the green box indicates the corresponding conditions, and the larger value between the two values in the red ellipses should be selected. Therefore, in the report above, the UGR value reported under DLC SSL is 29.7. This value is calculated based on luminous intensity distribution data measured by YIMING Technology goniophotometer, used to evaluate the glare level of luminaires.
Figure: DLC SSL UGR value selection method, showing how to obtain UGR values and select the correct value
