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Poor lighting can cause several problems such as:
This document summarizes general ways to detect and solve some of the more common lighting problems. Information on how to conduct a more detailed (or formal) lighting survey is located under How do you conduct a more detailed lighting survey?.
Poor lighting can be a safety hazard – misjudgment of the position, shape or speed of an object can lead to incidents and injury.
Poor lighting can affect the quality of work, specifically in situation where precision is required, and overall productivity.
Poor lighting can be a health hazard – too much or too little light strains eyes and may cause eye discomfort (burning, etc.) and headaches.
The amount of light we need varies and depends on:
The amount of light falling on a surface is measured in units called lux. Depending on the factors noted above, adequate general lighting is usually between 500 and 1000 lux when measured 76 cm (30 inches) above the floor.*
Examples of industrial and office tasks and the recommended light levels are in the table below.
|Recommended Illumination Levels*|
|Type of Activity||Ranges of Illuminations (Lux)**|
|Public spaces with dark surroundings||20-50|
|Simple orientation for short temporary visits||50-100|
|Working spaces where visual tasks are only occasionally performed||100-200|
|Performance of visual tasks of high contrast or large scale||200-500|
|Performance of visual tasks of medium contrast or small size||500-1000|
|Performance of visual tasks of low contrast or very small size||1000-2000|
|Performance of visual tasks of low contrast and very small size over a prolonged period||2000-5000|
|Performance of very prolonged and exacting visual tasks||5000-10000|
* From: IESNA Lighting Handbook. 9th ed. Illuminating Engineering Society of North America, 2000. p. 10-13.
**Lux = Lumens (quantity of light) per square metre.
To reach proper light levels and uniform light distribution in the visual environment, many light fixtures are designed to reflect light off walls, ceilings and objects. The amount of light reflected off a surface can be measured. Suggestions for the percent of light reflected off surfaces in a typical office include:
The percent value refers to the amount of light that a surface reflects relative to the amount that falls on the surface.
In addition, light fixtures that are too widely spaced or wrongly positioned can create shadows. Objects between the light fixture and work being done can block the light and cast shadows. Likewise, workers sitting with their backs to windows, with light fixtures directly overhead or to the rear, cast shadows on their own work surfaces.
To detect insufficient light, try the following:
Workers should sit in their normal working positions during measurement to give you accurate results.
To correct insufficient light:
Glare is a common lighting problem. Glare is what happens when a bright light source or reflection interferes with how you are 'seeing' an object. In most cases, your eyes will adapt to the brightest level of light. When this adaptation happens, it becomes harder to see the details in the duller or darker areas of the work space (even though they are actually sufficiently lit!). Glare can cause annoyance and discomfort, and can actually decrease a person's ability to see.
Reflected glare is caused by:
Direct glare is caused by:
There are several ways to find sources of glare.
To correct glare, try:
There are two types of contrast problems – the first occurs when there are very different light levels from one area to another, and the other is contrast between the colours of objects.
The immediate work area should be brighter than surrounding areas. If the surrounding area is brighter than the work area, your attention is distracted away from the work area.
The contrast between colours of objects, such as between the print itself and paper, or text and background on computer screens, can also cause problems. Too little contrast between print and the paper – or characters on a VDT screen and the background – makes reading tasks difficult. In an industrial setting an example would be that moving and stationary machine parts are hard to distinguish if they are the same colour.
To correct for poor contrast:
When light is poorly distributed, parts of the ceiling and general surroundings will seem dark and gloomy. Substantial differences in light levels force your eyes to readjust when moving from one light level to the other. Workers may find it difficult or impossible to see properly.
You can detect poorly distributed light by:
Correct for poorly distributed light by:
A complete lighting survey may be needed to identify and solve more subtle or complicated problems. A complete lighting survey requires complex equipment and practical experience.
Follow the manufacturer's instructions for the proper handling, care and maintenance of instruments. Many different techniques and instruments are available. Each of them has its own advantages and disadvantages.
A checklist is available in OSH Answers under "Lighting Ergonomics".
A complete basic lighting survey includes the following:
Illuminance is the amount of light falling on a surface. The unit of measurement is lux (or lumens per square metre = 10.76 foot candles, fc). A light meter is used to measure it. Readings are taken from several angles and positions.
Luminance is the amount of light reflected from a surface. The unit of measurement is candela per square metre (equals 0.29 foot-lamberts). An illuminance meter is used to measure it. Several measurements are made and averaged. Luminance tables are consulted for reference values.
Contrast is the relationship between the brightness of an object and its background. A luminance meter is used to measure it. The following formula is used to calculate contrast and provides a number between 0 and 1. The average contrast should be above 0.5:
Reflectance is the ratio of light falling on a surface to the light reflected from a surface, expressed as a percentage. A light meter is used to measure it. Reflectance can also be measured using a reflectometer or by comparing the surface of interest with colour chips of known reflectance.
To determine reflectance, the light meter probe is placed on the test surface to measure light falling on the surface. Next, place the probe 5-7 cm away facing the surface to measure the light reflected from the surface. The following formula is used to calculate reflectance: