For years, the conversation around lighting was dominated by lumens (brightness) and watts (energy consumption). While these are still important, focusing on them alone is like buying a car based only on its top speed—you’re ignoring the comfort, safety, and handling.

Glare, specifically disability and discomfort glare, is the visual experience caused by excessive and uncontrolled contrast between light and dark areas in your field of view. In an office, this often comes from a bright ceiling light reflecting on your dark computer screen. This is where UGR comes in—it’s the standardized way to measure this “discomfort.” People driving usually also come across the glare and it brings high uncomfortable light directly by car headlight.

The Simple Analogy: Car Headlights on a Dark Road

Think about driving at night. When an oncoming car has its high beams on, the glare is blinding. That’s a high-glare situation. Now, imagine that same car with its well-adjusted, modern low-beam headlights. You can see perfectly well without the discomfort. That’s a low-glare situation.

UGR works on a similar principle. It quantifies the level of discomfort glare caused by bright lights (the luminaires) in your visual environment relative to the background illumination.