Glare And Its Control

A good lighting system, as well as providing a suitable level of illumination, must avoid glare.
There are two types of glare: disability glare and discomfort glare.

Disability glare

The term 'glare' is usually thought of as the presence of a very bright light source, such as car headlights or the sun, which prevents us from seeing the necessary detail. This type of glare is known as disability glare, which impairs the ability to see the detail without necessarily causing visual discomfort. It is nearly always associated with excessive light received by the eye, either direct from the light source or by reflection from bright shiny surfaces.

Discomfort glare

This is defined as glare that causes visual discomfort without necessarily impairing the ability to see detail. It is therefore a less obvious type of glare and manifests itself in the form of discomfort.

Lighting systems in most interiors are more likely to cause visual discomfort than disability. The discomfort may not be apparent but it's effects are cumulative and contribute to a sense of tiredness, especially towards the end of the day. People with poor health are particularly sensitive to visual discomfort caused by glare, as are elderly people.

Control of glare

It is often possible to reduce or avoid glare by:

1. The reflection factor of the object and the immediate background should be adjusted so that the contrast is adequate for seeing the task without being so high as to cause discomfort.
2. Where local lighting is provided the surrounding general illuminance should not fall too low, i.e. increase the background illuminance to reduce glare effects. The area surrounding the task should be illuminated to not less than one-third of the task illuminance.
3. Shiny or specular surfaces should be avoided where there is the possibility of bright images being reflected; use matt surfaces.
4. Luminaries should be installed at correct mounting heights and spacing, otherwise uneven lighting will occur.
5. Source luminance should be kept at a minimum; use diffusers or screens.
6. The solid angle subtended by the source at the observer's eye must be kept at a minimum.
7. Move the glare source out of the line of sight. This is easy if the lamps are suspended
8. Visual tasks should not be located so that a window is near the line of sight. If this cannot be avoided the window should be screened to reduce its brightness.

The most common cause of glare from lighting installations is due to the direct view of bare fluorescent tubes or incandescent lights from the normal viewing angle. Uplighters are being used increasingly because they avoid glare by giving diffuse light. They are luminaries. that direct most of the light upwards on to the ceiling or upper walls to illuminate the
 working plane by reflection.

Several different types of light source are used in uplighters. Two most common sources are the incandescent tungsten halogen and the high pressure sodium deluxe discharge lamps. Most uplighters have a wide symmetrical light distribution (although this is reduced it they are wall mounted).