How to Manage Lighting During Visual Tasks

Lights are often switched on in the morning and left on until the end of work. This can be wasteful, as it may not be necessary for all the luminaires to be in use all the time.
For example, luminaires near the windows can be switched off when daylight is adequate for the task and local lighting can be switched off when the work station is not being used. There are three methods by which lighting systems may be controlled:

1. manual
2. automatic
3. processor control

Manual control

The manual control of the lighting system, for example by a foreman, may appear to be a cheap method of control, although this is not always the case. The lights will be switched on when the daylight is adequate but are llesss likely to be switched off when the daylight becomes sufficient. The control panels for work areas must be clearly marked so it is clear which switch controls which bank of lights or individual lights. It must be easily accessible and located in a convenient place.

Automatic control

This may be provided by photocells, which can monitor the level of useful daylight. These can either be of the type that simply switch on or off at preset levels or they may increase or decrease the electric light, so that a certain level of illumination is maintained. The photo-electric type of control which simply switches on or off, may control the whole working area or control only the lighting near to the windows. To prevent the lights from switching on and off because of passing clouds, they are usually fitted with a time delay. If dimming control is wanted then it should be noted that this may be used only with filament or tubular fluorescent lamps. This system is generally preferred by employees as the light increases or decreases slowly- there is no sudden switching on or off. Time switches may also be used to switch lights on at the start of the day and, most importantly, off at the end of the day. All too often lights are left on overnight- a waste of money and energy. A manual over-ride should be available, so that unexpected circumstances can be dealt with, such as maintenance or cleaning outside of normal hours. Other control devices can detect the presence of a person within an area and switch on the lights. These will then be turned off after the area has been vacated for a set time. These devices include audio, ultrasonic and IR sensitive systems.

Processor control

These systems, which are either computer or microprocessor-based are becoming more popular. They can not only control lighting, but also building services, such as air-conditioning, fire alarms and lifts. The great advantage of this system is its flexibility, in that the computer control programme can be adjusted to suit the work areas and can be modified as required. The system can monitor the building continuously, so that it is operating at maximum efficiency and economy.