Module 1: Occupational Hygiene - Section 5: Instrumentation

OH5.13: Principles of Illumination - Sources of Lighting

Sources of lighting

There are two different sources of lighting that are traditionally used in workplaces. They are natural (daylight) and artificial (electric) lighting. ³

Daylight:

The amount of daylight reaching an area or a workstation depends on the direction of sunlight, cloud cover, local terrain and season. The size, orientation and cleanliness of windows is also important. The amount of daylight can be controlled with tinted glasses, window blinds, curtains and awnings. Daylight is desirable in many workstations provided it does not cause glare.

Electric lighting:

Daylight does not provide constant illumination due to its wide variability. One can exercise greater control over illumination through use of artificial lighting. Electric lighting is the source of lighting that is generally used in industry, especially where employees have to work at night.

There are three basic types of artificial lighting:

• General lighting provides uniform lighting over the whole working plane. For example use of ceiling fixtures.
• Localised lighting systems provide illumination at general work areas with simultaneously reduced level of lighting in adjacent areas. Overhead fixtures are used to increase lighting levels for particular tasks.
• Local lighting systems provide illumination for relatively small areas incorporating visual tasks. This is achieved by increasing light levels over the work area. This allows the user to adjust and control lighting.

Types of artificial lighting:

Selection of light sources is based on capital costs, efficiency, installation, running costs, maintenance, life characteristics, size, robustness, and heat and colour output.

Light sources can be divided into two kinds, namely, incandescent and fluorescent lamps. ¹

Incandescent lamps:

A filament inside the bulb is heated to a high temperature by passing an electric current through it. The light of the filament is relatively rich in red and yellow wavelengths. The advantage of filament lamps is that they give light immediately after they are switched on. Examples of incandescent lamps are the common light bulb, reflector bulbs and halogen bulbs. Incandescent lamps are generally used in households.

Incandescent lamps are cheaper to buy and to install, however, they require frequent replacement. The temperature increases around the lamp can reach 60 ºC and can cause discomfort and headaches, especially for office workers.

Fluorescent lamps produce light by passing a electric current through a gas (argon or neon) or through mercury vapour in a glass tube coated with fluorescent material. These lamps have greater efficiency than incandescent lamps and a longer life. They come to full light output reasonably quickly.

Fluorescent lamps are costly to install and when they are old or defective the tubes develop a slow visible flicker. Flickering light can be annoying and can cause visual discomfort. Examples of fluorescent lamps are high-pressure sodium lamps (glass arc tube) which are mainly used in factories and commercial buildings, and low pressure sodium lamps (tubular fluorescent) that are generally used on roadways.

General Introduction to Occupational Health: Occupational Hygiene, Epidemiology & Biostatistics by Prof Jonny Myers is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License