Ever installed a light that looked perfect on paper but caused glare on-site? You’re not alone. Ignoring UGR can lead to eye strain, poor lighting, and unhappy clients. Let’s fix that.

UGR, or Unified Glare Rating, measures the discomfort glare from a lighting installation. Contrary to what many believe, UGR is not a fixed value of the luminaire—it depends heavily on the environment, layout, and observer position. It helps designers maintain visual comfort, especially in offices, schools, and commercial spaces. Understanding UGR allows better design choices for both aesthetics and functionality.

Ready to learn how UGR really works and why it’s not set in stone?

What is the UGR value?

UGR stands for Unified Glare Rating. It’s a way to measure how much glare a person might experience from a lighting setup. The number helps determine how comfortable the lighting will feel to someone working or sitting in that space. The scale goes from 10 to 30. A value of 10 means there’s basically no glare at all, while 30 means the glare is likely to be very uncomfortable.

For places like offices, classrooms, and meeting rooms, a UGR value of 19 or lower is usually recommended. This level keeps eye strain low and creates a more comfortable visual environment. But the UGR value doesn’t just depend on the light fixture itself. It also depends on things like how the room is designed, how reflective the walls and ceilings are, and even where the person is sitting or standing.

So, the same light installed in two different rooms could have totally different UGR results. That’s why proper lighting design is important—not just picking a good fixture, but also thinking about how it fits into the overall space.

Is UGR A Fixed Value?

No, UGR is not a fixed value. That’s a common misunderstanding I run into all the time. You’ll often see lighting products labeled with something like “UGR<19,” and while that sounds definitive, it’s not the full picture. That number usually comes from a simulation in a standard test room. It’s just an estimate, not a guarantee.

The real UGR depends on how and where the light is installed. It’s calculated using a formula that takes into account the size and shape of the room, how reflective the walls and ceiling are, and even where the person is located in the space. Change any of those things, and the UGR changes too.

So when someone asks me, “What’s the UGR of this fixture?” I always tell them: it depends. It depends on the installation, the layout, and the environment. You need to evaluate the whole setup to know the actual UGR.

How to calculate UGR value?

UGR, or Unified Glare Rating, is calculated using a detailed formula created by the CIE (International Commission on Illumination). The formula considers several things: the brightness of the light source, the angle between the observer and the light, the background brightness, and even the position of the observer.

But here’s the thing—it’s not something you can figure out with a pocket calculator. You need real data and a full room layout to do it properly. That’s why most professionals turn to lighting simulation software like DIALux or Relux. These programs model the actual space, taking into account room dimensions, wall and ceiling reflectance, and fixture placement. They then simulate how light behaves in the space and calculate the UGR from the observer’s viewpoint.

If glare is a concern—say, in offices, classrooms, or control rooms—it’s essential to run a simulation. Otherwise, you’re just guessing, and the result could lead to uncomfortable lighting conditions for the people using the space. Learn more about How is UGR calculated?

What is the UGR rating of lights?

You’ll often see lights advertised with UGR ratings like “UGR<19” or “UGR<22.” But remember—that’s just in ideal test conditions. The manufacturer runs a simulation in a standard room size (like 4H x 8H) with typical reflectance levels and gives you the best possible result. It’s useful as a benchmark, but not gospel. UGR lighting design means thinking beyond the brochure and into your real-world installation.

UGR values for different applications

Unified Glare Rating (UGR) helps determine how comfortable lighting will feel to people in a space. Different environments require different glare levels depending on how critical visual tasks are. Here’s a breakdown of what UGR values work best for various settings:

• UGR < 10: This is top-tier visual comfort. It’s usually required in environments like museums or galleries where lighting needs to be soft, precise, and easy on the eyes.
• UGR < 16: Ideal for control rooms, inspection areas, or places where workers spend long hours focusing on fine details. Low glare is a must to prevent fatigue and mistakes.
• UGR < 19: Commonly recommended for offices, classrooms, and study areas. It ensures visual clarity without distracting or tiring glare.
• UGR < 22: Suitable for public areas like lobbies, waiting rooms, or hallways where people don’t stay long and glare tolerance is higher.
• UGR < 25: Acceptable for industrial zones, workshops, or outdoor applications. These are environments where people move frequently and don’t rely on precise visual work.
• UGR > 28: Generally too high for any interior space. This level of glare can cause discomfort, distraction, and even headaches in sensitive environments.

Remember, UGR is not just about the light fixture itself. The room’s layout, the surface finishes, and even where people are sitting or standing all affect the final UGR. So, while these values serve as a good reference, real-world testing or simulation is the best way to confirm you’re hitting the right target for your application.

What is the difference between UGR and glare rating?

UGR is a standardized metric defined by the CIE, used for indoor lighting. It calculates the discomfort glare from an observer’s point of view. Glare rating, on the other hand, is a broader term and may include other types of glare, such as disability glare or veiling reflections. UGR is about how uncomfortable the light feels. It doesn’t account for loss of visibility, only how annoying the light is to your eyes. So while all UGR is about glare, not all glare ratings are UGR.

What is the UGR 19 rating?

UGR 19 is widely accepted as the standard for office lighting. It means the lighting setup creates low enough glare to keep people comfortable while working on tasks like reading, typing, or using a computer. When lighting designers say they’re aiming for UGR 19, they’re targeting a level that minimizes visual strain and distraction in spaces like offices, classrooms, and meeting rooms.

But here’s what most people miss—UGR 19 is not just about picking a light fixture labeled “UGR<19.” That label is based on a simulated environment, not your actual space. To truly achieve a UGR below 19, you need to consider the full picture: ceiling height, surface reflectance, desk layout, and fixture positioning.

For example, placing a low-glare fixture in the wrong location can still lead to uncomfortable reflections on screens or shiny surfaces. On the flip side, a well-designed room using standard fixtures can still maintain a UGR below 19 if everything is planned correctly.

So, reaching UGR 19 takes more than choosing the right fixture—it requires smart lighting design, accurate room modeling, and attention to how the space will actually be used. That’s why lighting simulations and design software are key tools when visual comfort really matters.

Conclusion

UGR is not a fixed number tied to the light fixture—it’s a dynamic value shaped by real-world conditions. Misunderstanding this can lead to uncomfortable lighting and unhappy users. So if you care about visual comfort, simulate before you specify. Match the fixture to the room, not just the label.

Got questions about selecting the right UGR LED fixture for your space? Reach out—we’re here to help you create lighting that works.