With conventional switching, people switch on lights when they are needed but do not switch off. There is now available a range of control systems which can automatically operate the lighting but still retain a manual over-ride.

Time Control

This can be a simple clock mechanism similar to that on a video recorder. The lighting can be programmed to come on at set times during the week to coincide with normal operating hours. Such a control can also be part of a computerised building management system which monitors all services. Occupational Control This detects whether people are present in the space and switches off the lighting accordingly Usually there is a short time delay so if an office is vacated the lighting will only be switched off if nobody returns in, say, 10 minutes. Most offices have members of staff away from their work station for at least 30% of the working day due to off-site visits, training or absence. With the correct level of control the lighting of the unoccupied areas can be switched off automatically. Passive infra-red detectors are usually used but sonic devices are also available.

Natural Daylight

The availability of daylight will vary with the position in a building, the time of day, weather conditions, and the seasons. Photo-cells can detect and measure the amount of natural light entering a building and switch, or even dim, the artificial lighting to retain a suitable balance. Because daylighting can vary very rapidly dimming is particularly useful as the changes are much less noticeable than frequent on/off switching. The type of control system will depend upon the type of building and occupancy pattern. Such control can be applied to new buildings and retro-fitted to existing installations.

Bulk Lamp Replacement Lamps will fail individually, even when operated on the same switching cycle. The rate of failure will increase with age. Bulk replacement is more cost effective than spot replacement and provides a more uniform lighting system. However, where automatic switch controls such as just described are in use, the burning hours of lamps will vary considerably and spot replacement will be required. Even so there is usually an economic case for bulk replacement to coincide as part of the routine luminaire cleaning programme. The cost of lamp replacement depends upon the type of installation as well as the type of lamp. Also the cost of interrupting the normal working in the space has to be considered. Each situation has to be separately assessed and it is not possible to offer generalised recommendations.