What is UGR in Lighting?

Do you struggle with glare in your lighting design? Poor glare control can lead to discomfort and even decrease productivity. This issue is especially important for office spaces, retail stores, or any environment with extended lighting use. The Unified Glare Rating (UGR) system is a solution to measure and reduce glare, creating a comfortable, efficient space. In this article, we’ll explain UGR, why it matters, and how to achieve optimal glare control in your lighting design.

The Unified Glare Rating (UGR) system measures the discomfort caused by lighting glare, ranging from 10 to 30. A lower UGR value indicates more comfortable lighting, while higher values suggest excessive glare that can impair vision and reduce productivity. UGR is essential in environments like offices, schools, and factories to ensure visual comfort and safety. Developed by the International Commission on Illumination (CIE), UGR helps designers create lighting systems that minimize glare and improve comfort, especially in spaces with prolonged lighting exposure.

Let’s dive into the concept of UGR, why it’s so important, and how you can improve your lighting designs by managing glare.

What is the Unified Glare Rating System?

The Unified Glare Rating (UGR) is a scale used to measure the discomfort caused by lighting glare. The UGR system quantifies glare from a lighting fixture, considering factors such as brightness, angle, and the layout of the light source in relation to the observer. UGR values typically range from 10 to 30, where lower values are better. A high UGR indicates significant glare, while a low UGR means the lighting is comfortable and reduces visual discomfort. This system is commonly used in indoor environments, particularly in office and commercial settings, where prolonged exposure to lighting glare can negatively impact comfort and productivity.

1. What is Glare?

Glare refers to intense light that causes discomfort or impairs vision. It can be caused by direct light sources, like bulbs or fixtures, or by reflections from shiny surfaces. Excessive glare can lead to reduced productivity, eye fatigue, and even accidents in workplaces.

2. UGR Rating Scale

The UGR is a numerical rating scale, usually ranging from 10 to 30. The higher the UGR value, the greater the level of discomfort glare. Here’s a basic idea of what the values mean:
– UGR 10-16: Very low glare, comfortable for most environments.
– UGR 16-19: Low glare, suitable for general office lighting.
– UGR 19-22: Moderate glare, might cause discomfort in some cases.
– UGR 22-25: High glare, uncomfortable for most people, especially in detailed tasks.
– UGR 25+: Very high glare, often unacceptable for any indoor working conditions.

These calculations are typically done using specialized software or formulas that account for the geometry and lighting parameters of the space.

3. Applications of UGR

UGR is often used in environments such as:
– Offices: Where workers need to focus on screens or detailed tasks.
– Schools and Classrooms: Ensuring that students are comfortable and not distracted by overly bright lights.
– Retail Spaces: To avoid creating uncomfortable shopping conditions.
– Factories: Where glare could interfere with workers’ safety.

Where did UGR originate from?

UGR was developed by the International Commission on Illumination (CIE), a global organization that defines lighting standards. The goal of the UGR system was to standardize the measurement of glare and provide a reliable method for designing lighting systems that minimize discomfort. The concept of UGR originated from the need to create better lighting for people working in indoor spaces, ensuring that lighting designs were not just functional but also comfortable for the eyes. It has since become a key aspect of modern lighting design, especially with the rise of LED lighting systems that can cause higher glare if not properly controlled.

Why is UGR important to consider in lighting design?

UGR is a crucial factor in lighting design because it directly impacts the comfort and well-being of individuals in a space. High glare levels can cause visual discomfort, leading to headaches, eye strain, and decreased productivity. This is especially important in offices, retail spaces, and educational environments, where people spend long periods under artificial lighting. Managing UGR ensures that the lighting is pleasant and effective, improving visibility without causing strain. By using the UGR system to guide your lighting design choices, you can create more comfortable, user-friendly environments that enhance overall experience and performance.

How is UGR calculated?

UGR is calculated based on a formula that takes into account the luminance of light sources, their position relative to the observer, and the angle at which the light hits the observer’s eye. The formula involves the brightness of the light sources, the reflection of light from surfaces, and the overall layout of the room. UGR values are typically calculated using specialized software, which simulates different lighting setups and calculates the resulting glare. Understanding the calculation of UGR allows designers to create more precise and efficient lighting designs that meet comfort and performance standards.

To calculate the UGR value, apply the following formula:

UGR Calculation Formula

• 8: A constant factor used to scale the result, ensuring the UGR falls within a range of 10 to 30.

• ∑: The summation sign, representing the total glare effect from each visible luminaire.

• lg: The common logarithm, used to account for the human eye’s logarithmic perception of brightness.

• Lb: Background luminance, which determines how well the eyes are adapted to the ambient light in the space.

• Ls: The average luminance of each individual luminaire, which represents its brightness.

• Ω: The solid angle of the light-emitting parts of the luminaire, measured from the observer’s position. This indicates the size of the glare-producing light source.

• ρ: The Guth index, which measures the luminaire’s position relative to the observer’s line of sight, affecting the glare intensity perceived.

What is a UGR table?

The UGR table value is not a direct technical feature of a luminaire, but rather a measure used to assess the glare impact from a specific observer’s perspective and the position of the luminaire. The UGR table method can be a helpful tool in lighting design, assisting in the selection and comparison of different luminaires.

By using standard lighting calculation software, the luminous intensity distribution of a luminaire can be analyzed to create a table of UGR values. This table reflects various standardized arrangements of the luminaire in a rectangular room with set proportions. The values are determined based on different levels of room surface reflectivity and the orientation of luminaires relative to the observer’s line of sight.

The calculation is typically done for the worst-case scenario, where the observer is positioned on the wall to maximize the number of visible luminaires. For example, if the UGR value for two specific geometries is no higher than 19.4, the luminaire is assigned a UGR value of 19, making it suitable for office environments.

UGR(Unified Glare Rating) Table

What UGR levels are recommended?

The recommended UGR level depends on the type of environment and the activity taking place. For most office spaces, the ideal UGR level is below 19 to ensure visual comfort and reduce glare. For areas such as classrooms or meeting rooms, a UGR value between 13 and 19 is recommended. Higher UGR values, such as those above 22, are typically considered uncomfortable and can lead to fatigue or headaches. In spaces with LED lighting, it’s important to pay close attention to UGR levels since LEDs can often produce higher glare if not properly designed. Managing UGR levels ensures a pleasant and productive environment.

Here is a simplified recommendation table for maximum allowed UGR values based on the type of area:

What does UGR19 mean?

UGR19 refers to a UGR value of 19, which is considered the standard for comfortable indoor lighting. A UGR of 19 or lower indicates that the lighting design provides minimal glare and is suitable for office and commercial spaces where people spend extended hours. At this level, the lighting is bright enough for visibility without causing discomfort or fatigue. Achieving a UGR of 19 is especially important for environments with high visual tasks, such as offices, workstations, and schools, where glare could interfere with productivity and concentration.

How to Reduce UGR (Unified Glare Rating)

Reducing the Unified Glare Rating (UGR) in lighting design is essential to ensure a comfortable and productive environment. High UGR levels can cause discomfort, eye strain, and reduce overall effectiveness in spaces like offices, schools, and factories. Here are several strategies to reduce UGR and improve visual comfort:

1. Use Indirect Lighting

Indirect lighting, where the light source is reflected off ceilings or walls, helps diffuse light more evenly across the space. This reduces harsh shadows and minimizes the intensity of direct light that can cause glare. By bouncing light off larger surfaces, the light is more spread out, reducing the UGR value.

2. Select Luminaires with Lower Luminance

Choose luminaires with a lower luminance, as high luminance from a light source can significantly contribute to glare. Luminaires with diffusers or lenses that spread the light evenly can reduce the brightness intensity and help in lowering the UGR.

3. Position Lights Strategically

The positioning of light sources plays a crucial role in glare reduction. Avoid placing luminaires directly in the line of sight of the observer. Position lights at angles that minimize direct light hitting the eyes. Placing lights high up on the ceiling or in corners can also help reduce the glare effect.

4. Control Light Distribution

Use luminaires with controlled light distribution. Luminaires that direct light downwards, such as recessed lighting or wall-mounted fixtures, can reduce glare in areas like offices or classrooms where focused, task-oriented lighting is required. Avoid fixtures that scatter light in all directions.

5. Use Dimmer Controls

Implementing dimmable lighting allows the lighting intensity to be adjusted based on the time of day or activity. Dimming lights can help control glare, particularly in environments where lighting needs change throughout the day.

6. Reduce Room Reflectivity

The reflectivity of the room surfaces, such as walls, floors, and ceilings, can amplify glare. By using matte or low-reflective finishes for walls and ceilings, the glare effect is minimized. Glossy surfaces reflect more light and can increase the overall glare in the space.

7. Choose Lights with a Higher UGR Rating

While this may seem counterintuitive, using lights with a higher UGR rating might not always be harmful if they are positioned properly. Select luminaires designed to reduce glare with features like diffusers or special lenses that minimize direct brightness exposure.

8. Use Task Lighting

In areas such as offices or workstations, using task lighting—focused lights over desks or work surfaces—can help reduce glare in the general lighting while providing adequate brightness for specific tasks. This reduces the need for high brightness across the entire room.

9. Opt for LED Luminaires with Low UGR Ratings

LED lights typically have lower UGR ratings compared to traditional light sources. When selecting LED luminaires, opt for those specifically designed to minimize glare. These often feature advanced optics and diffusers that evenly distribute light and prevent harsh light spots.

10. Optimize the Room Layout

Adjust the layout of the room to ensure that light fixtures are placed in locations where they are less likely to cause direct glare. In spaces like offices, consider positioning desks and workstations in a way that minimizes direct exposure to light sources.

By considering the above strategies, you can reduce UGR and create more comfortable, glare-free environments. The goal is to provide adequate lighting for tasks while ensuring that lighting levels remain comfortable and conducive to both work and relaxation. A careful balance of luminaire selection, positioning, and room design can lead to a significant reduction in UGR, improving visual comfort and overall well-being.

Conclusion

Managing UGR in lighting design is essential for creating comfortable and functional spaces. By understanding the UGR system and applying it to your lighting choices, you can minimize glare and enhance the visual experience for people in your facility. Whether you’re designing an office, a school, or a commercial space, keeping UGR levels below 19 is crucial for ensuring comfort and productivity. Proper glare control leads to better well-being, greater focus, and improved overall performance.

If you need help or have questions about designing glare-free lighting, feel free to reach out to us directly. Our team of experts is here to help.