GLARE

Regardless of the light source or the direction from which the light comes, we often find direct light shining into our eyes extremely unpleasant. Bright light in particular, which often produces high localised illuminance levels, increases the risk of harmful glare. 

WHAT EXACTLY IS GLARE? 

Glare is described as a visual disturbance that significantly affects or impairs vision. 

There are essentially two types of glare: 

1. direct glare 
2. indirect glare 

Direct glare is caused by a light source shining directly towards the eyes. The eye must constantly compensate for large differences in brightness and consequently tires more quickly. Direct glare often leads to poor concentration and fatigue, particularly in the workplace. This is because it is not possible to quickly move out of the way or change the lighting conditions.

1 – direct glare
2 – indirect glare

Indirect glare is caused by reflections and backscatter from reflective and shiny surfaces. Such indirect glare is particularly tiring at a computer workstation, as the eye tries to ‘block out’ the reflection and focus on the monitor’s display. This not only leads to headaches and fatigue, but sometimes even to postural problems, as people try to avoid the reflections by adopting poor posture. 

You can read a few helpful tips on lighting at computer workstations here.

PHYSIOLOGICAL AND PSYCHOLOGICAL EFFECTS OF GLARE 

When considering the effects of glare, a distinction is also made between two categories: 

1. Physiological glare:
   This has an active, immediate and measurable effect on visual performance. Contrast and shape recognition are significantly reduced. 
2. Psychological glare:
   This refers to a reduction in visual comfort. This type of glare cannot be measured, as it is based on subjective sensitivity to disturbance. Psychological glare is often perceived subconsciously and thus interferes with the processing of information.

THE UGR VALUE 

The psychological glare value is referred to as the UGR value. It was established by the CIE to assess glare in a room. The DIN standard EN 12464-1 defines values from 10 to 30, where 10 stands for ‘no glare’ and 30 for ‘unacceptable psychological glare’. 

Standard UGR levels are 13, 16, 19, 22, 25 and 28. 

These are derived from statistical surveys and studies. Many participants were asked about the lighting conditions in the same room and expressed their subjective perception on a scale. This made it possible to calculate an average range within which the values should fall. 

In general: the higher the UGR value, the greater the glare. 

This value plays a major role in lighting design for workplaces, as certain maximum values are prescribed depending on the activities carried out.

At home, many things tend to happen intuitively. After all, we are much more flexible when it comes to the use, positioning and type of light sources. Nevertheless, some technical data sheets include the manufacturer’s specification for the UGR value. This serves primarily as a comparative figure for different light sources. A light source with a UGR of 16 will certainly cause less glare than one with a UGR of 25.