Module 1: Occupational Hygiene - Section 5: Instrumentation

OH5.15: Principles of Illumination - Lighting Issues

Factors of good illumination:

Factors to be considered are quality and quantity.

Quantity is the amount of illumination that produces brightness on the task and surroundings. The desirable quantity of light for any particular installation depends primarily upon the work to be done. Highest illumination levels are prescribed for tasks involving discrimination of fine detail, low contrast and prolonged work periods. More casual or intermittent tasks having high contrast are assigned lower values.

Quality pertains to the distribution of brightness in a visual environment (colour of light, its direction, diffusion, degree of glare). The term is used to ensure that all brightness contributes favourably to visual performance, visual comfort, ease of seeing and safety.

Lighting for movement in and around buildings:

Passages and stairs:

Accidents can happen when people move from bright to dark areas such as passages (the time needed for eyes to adjust may be too long). Therefore, passages should have relatively higher levels of illumination. Also, one should prevent disturbing glare caused by direct observation of bright light sources.

Entrances:

There is a danger of accidents occurring if entrances, and especially stairs, are poorly lighted. This may be overcome by positioning windows to let in enough natural light at the entrance or by the installation of artificial lighting. For safety reasons, it is advisable to illuminate the area outside the exit at night.

Emergency lighting:

An interruption of the main lighting supply can be very dangerous. The accident risk is high in industrial sites due to presence of potentially dangerous installations. Emergency lighting from an independent source has to be provided. Sufficient emergency lighting has to be provided for First Aid posts, and for the safe exit from the building.

Maintenance of light fixtures:

Dust and dirt are deposited on all room surfaces and glasswork. This results in a decrease in the transmission of light. Effective maintenance requires replacement of lamps when their time of economic usefulness is expired, and regular servicing and cleaning of light fittings.

Replacement of lights in batches is advantageous:

• for large installations when luminaires are mounted at a substantial height;
• when maintenance is only possible at long intervals; and
• replacement of lamps can be combined with planned programme for cleaning of luminaires.