Understanding Unified Glare Rating (UGR) in Lighting

A comfortable working environment is critical for optimal productivity. Well designed lighting in our spaces can help achieve a comfortable working environment. One critical factor in reducing eye fatigue is glare – which can best be described as excessive brightness or discomfort caused by light sources

What is the Unified Glare Rating? The Unified Glare Rating (UGR) predicts the glare caused by an electric lighting system along a psychometric scale of discomfort. In simpler words, UGR predicts the amount of discomfort causing glare produced by a lighting installation for a fixed set of conditions. Discomfort glare can result in annoyance, headaches or eyestrain. Discomfort glare is different from disability glare, which impacts the viewer’s ability to discern objects accurately. UGR is a measure of discomfort glare, not disability glare.

How Is UGR Calculated?

The calculation method for UGR only provides meaningful results for mainly direct distribution light sources. It only takes into account direct glare from light sources, but not reflected glare caused by reflections on surfaces. Please note, when selecting lighting solutions for educational and office environments, it’s essential to consider all factors beyond glare, including performance, lighting level, comfort, colour rendering, uniformity, direction, colour, shadow and ambience.

The level of UGR ranges from 40 (high glare) to 5 (low glare). The lower the UGR, the better. A recommended UGR range typically falls
between 16 and 19 for office and educational settings. However, this range should be approached as a guideline rather than an absolute rule.

It’s important to recognise that the optimal UGR can vary depending on influencing factors specific to each environment, and therefore, UGR should be used intelligently with an understanding of the unique characteristics of each surrounding.

Why UGR Matters

Excessive glare can lead to headaches, eye strain, and even long-term vision problems. In workspaces, it can reduce productivity and focus. In schools, it can hinder concentration and learning. By incorporating UGR into lighting design, architects and engineers can ensure that spaces are not only well-lit but also visually comfortable.

Best Practices for Managing UGR

1. Use Diffused Lighting: Fixtures with diffusers or indirect lighting can help distribute light more evenly and reduce high-luminance spots.

2. Proper Placement: Position light fixtures to avoid direct lines of sight from common working positions.

3. Task Lighting: Use adjustable, localized lighting instead of increasing general lighting levels.

4. Simulation Tools: Leverage lighting design software to model glare and evaluate UGR before installation.

How to Control UGR in Lighting Design

There are several ways to reduce glare from light sources:

Beam Angle

Lighting beams play a significant role in reducing glare. By carefully controlling the direction and intensity of a luminaire’s beam, you can direct light where it’s needed without causing discomfort to the user.

Surface Reflectivity

The interaction between light and surfaces can sometimes lead to unwanted reflected glare. This occurs when light bounces off surfaces. However, it’s possible to effectively minimise glare by ensuring surface uniformity and consistent luminance while maintaining the same lumen output.

Visibility

Light sources that are visible to the eye can amount to glare and cause discomfort. Shading and shielding light sources prevent the harsh, blinding sensation that often accompanies glare.

LIGHTING Placement

Placement of a light source is often an effective technique to minimise glare. Each space will have an appropriate height and angle for where light sources should sit, which can help prevent light from directly hitting the line of sight. In particular environments, such as classroom reading areas and workspaces, this is especially important.

 

Ambient Light