UGR (engl. Unified Glare Rating) is a meter used in lighting that evaluates the amount of glare in a space. It helps determine how disturbing or unpleasant people find the lighting. The UGR value is especially important in offices, schools and other workplaces where glare can reduce work efficiency and comfort.

Meaning and calculation of UGR value

The UGR value is based on a complex calculation formula that takes into account several factors:

• The brightness of the luminaires
• Placement of luminaires
• Light direction
• Reflectivity of space and surfaces
• The position of the lights and the viewer in relation to each other

Based on these factors, it is calculated how much the glare from light sources irritates the people in the room. The higher the UGR value, the greater the glare experience.

UGR values ​​and their meaning:

UGR < 10: There is very little or no glare. This is suitable, for example, for spaces where very soft and even lighting is needed.

UGR 10–16: Glare is low and is usually not perceived as disturbing. This is a good lighting requirement for meeting rooms or office spaces, for example.

UGR 16–19: Glare is moderate. This value is suitable for most work environments, such as open-plan offices.

UGR 19–22: Glare can be a bit disturbing, but usually still tolerable in, for example, industrial and warehouse spaces.

UGR 22–25: Glare is already noticeable and can interfere with working.

UGR > 25: Häikäisy on erittäin häiritsevää ja epämukavaa, ja se voi haitata merkittävästi keskittymistä ja työntekoa.

The UGR value (Unified Glare Rating) is not measured directly from the lamp, but is calculated from certain characteristics of the lamp and the space using a mathematical formula. Calculating the UGR value requires certain information about the space, the placement of the lamps and the characteristics of the light. It is therefore a calculated quantity based on several different factors, and it cannot be directly measured with, for example, a light meter.

Factors needed to calculate the UGR value

Here is the calculation formula:

The UGR value is calculated based on the following factors:

1. Brightness of the lamps (L): The brightness of the light source (luminance), i.e. how much light the lamp emits in the direction of the viewer.
2. Position of the viewer (Ω): The position of the light sources in relation to the viewer. This is also related to where the lights are in the viewer's field of vision and what size they appear to be.
3. Backlight (L_b): Ambient lighting level, i.e. how brightly the surrounding surfaces are illuminated. The glare is stronger if the lamps stand out significantly brighter than the surrounding surfaces.
4. Number of lamps (p) and location: How many lamps are in the space and how they are placed. The more lights are in the viewer's field of vision, the greater the glare may be.

The process of measuring the UGR value

Since the UGR value is based on a complex formula and several different parameters, specialized lighting design programs such as DIALux, Relux or other CAD-based lighting calculation programs are often used to calculate it. These programs are entered into:

• Technical data of the lamp (luminance distribution, type of light sources, etc.)
• Room dimensions and reflectivity
• Placement and height of the lamps

Based on this information, the program calculates the UGR value in different places of the room and gives an estimate of how disturbing the glare is from different perspectives.

Summary

• The UGR value is not measured directly from the lamp, but is calculated based on the lighting conditions and the characteristics of the room.
• The calculation is based on the brightness of the luminaires, their placement and the surrounding lighting.
• The UGR value is calculated using specialized lighting design programs based on accurate measurements and data.