The glare factor and Unified Glare Rating ( UGR ) are both metrics used to quantify and assess the level of glare from lighting, but they differ in how they are calculated and applied.
UGR (Unified Glare Rating)
The UGR is an internationally recognized measure of the amount of glare caused by lighting, particularly in workspaces and offices . It is used to assess whether the lighting in a space is comfortable for the eyes of users, without causing reduced visibility or discomfort.
UGR scale:
- UGR is calculated on a scale of 0 to 40, with a low UGR indicating little glare and a higher UGR indicating more glare.
- UGR values are calculated based on factors such as the position of the light source , the brightness of the light , the distance to the source , the surrounding environment and the angle of the light rays .
UGR values and their impact:
- UGR < 19 : Very low glare (for example in areas where there are no lighting requirements, such as homes).
- UGR 19-22 : Low glare (comfortable for most office environments).
- UGR 22-25 : Moderate glare (may be uncomfortable for prolonged visual activities).
- UGR > 25 : High glare (usually not suitable for work areas, causes discomfort).
Glare factor
Glare factor is a more general measure used to evaluate how much illumination can directly disturb the eyes . It refers to the relative brightness of a light source within an observer's field of view and how that affects visibility and comfort.
Glare factor and UGR comparison:
- The glare factor can be thought of as the direct experience of bright light entering the field of view and thus obstructing vision.
- The UGR is a more scientific and quantitative measure of the same disturbance, using a specific formula and taking into account the placement of light sources and other environmental factors.
Difference between UGR and glare factor
- Calculation :
- UGR is calculated using a specific formula that takes into account factors such as light intensity, viewing angle, position of light sources and reflections from walls and ceilings.
- The glare factor is usually a more subjective assessment that depends on the intensity of the light and the angle of the light source.
- Application :
- UGR is often used in office environments and workspaces to create a comfortable working environment by minimizing glare.
- The glare factor is used in more general situations, such as the assessment of street lighting, car lighting , or other lighting systems outside workplaces.
Example: UGR in an office
In an office where employees work on computers, for example, the lighting should be chosen to keep the UGR below 19 to minimize the glare factor. This means that the lighting in the office should not be too bright or positioned in a way that compromises employees' vision, such as by placing light sources directly in their field of vision.
How UGR and glare factor influence design
- Lighting design : In modern lighting designs, great attention is paid to the UGR value and minimizing the glare factor . For example, the placement of lighting should be chosen so that it does not shine directly on the user's face. This can be achieved through shielded fixtures , diffusers , or dimmable systems that regulate light intensity as needed.
- Health and wellbeing : Minimising glare and maintaining low UGR values contributes to a healthier working environment by reducing eye strain, preventing headaches and reducing eye fatigue .
Summary
- UGR (Unified Glare Rating) is a standardized way to measure glare in workspaces, based on scientific calculations and various environmental factors.
- Glare factor is a broader term that refers to the amount of distracting illumination in a person's field of view.
- UGR is often applied in office environments and workspaces, while glare factor can be used more widely, including public lighting and vehicles.
Both concepts are essential for creating comfortable lighting conditions , both in workspaces and in other environments where lighting influences people's well-being.