Lighting Ergonomics - Survey and Solutions

What are some of the most common lighting problems?

Poor lighting can cause several problems, such as: This document summarizes ways to detect and solve common lighting problems.

• context Insufficient light – not enough (too little) light for the need.
• context Glare – too much light for the need.
• context Improper contrast.
• context Poorly distributed light.
• context Flicker.

What are other OSH Answer documents about lighting?

Please also see:

• context Eye Discomfort in the Office
• context Lighting Ergonomics - General
• context Lighting Ergonomics - Checklist
• context Lighting Ergonomics - Light Flicker
• context Office Ergonomics - Computer Monitors and Display Colours

What should you know about insufficient light?

• context Poor lighting can be a safety hazard – misjudgment of the position, shape or speed of an object can lead to incidents and injury.
• context Poor lighting can affect the quality of work, specifically in situations where precision is required, and overall productivity.
• context Poor lighting can be a health hazard – too much or too little light strains eyes and may cause eye discomfort (burning, etc.) and headaches.

How much light is needed for various situations or activities?

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. * From: IESNA Lighting Handbook. 9th ed. Illuminating Engineering Society of North America, 2000. p. 10-13, CSA Z412:24 Office ergonomics - An application standard for workplace ergonomics, and British Columbia Occupational Health and Safety Regulations, Section 4.65 **Lux = Lumens (quantity of light) per square metre.

• context Type of task being done (such as demands for speed and accuracy).
• context Type of surfaces (does it reflect or absorb light).
• context General work area.
• context Individual's vision.

Should the surrounding environment be considered?

Yes. 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. To minimize glare, consider using work surfaces (such as the desk or documents) that are matte (less reflective) where possible. In addition, light fixtures that are too widely spaced or wrongly positioned can create shadows. Objects between the light fixture and the 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.

• context Window blinds (40-50%).
• context Walls (50% maximum).
• context Business machines (50% maximum).
• context Ceiling (70-80%).
• context Floor (20-40%).
• context Furniture (25-45%).

How do you test and correct for insufficient light problems?

To detect insufficient light, try the following: Workers should sit in their normal working positions during measurement to give accurate results. Determine the type, speed, and accuracy needed to do the task. Take into account individual factors, such as workers' age and vision needs, as well as any visitors or clients who may need to perform tasks. To correct insufficient light:

• context Measure the average illumination throughout the workplace. Compare this to the recommended levels.
• context Look for shadows, especially over work areas and on stairways.
• context Ask workers if they suffer from eye strain, squint to see, or get frequent headaches.
• context Replace bulbs on a regular schedule. Old bulbs give less light than new ones, so replace them before they burn out. Follow manufacturers' instructions.
• context Clean light fixtures regularly. Dirt on light fixtures reduces the amount of light given off. Light fixtures with open tops allow air currents to move dust up through the fixtures so dust and dirt do not accumulate on them.
• context Add more light fixtures in appropriate places.
• context Paint walls and ceilings light colours so light can be reflected.
• context Use more reflected light and local lighting to eliminate shadows. For example, a covered light mounted under a transparent guard on a grinding wheel provides the added light needed to clearly see the task.
• context Do not position the work station with the light fixture directly behind worker.

What should you know about glare?

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:

• context Light reflected from polished, shiny or glossy surfaces.
• context Glass on picture frames or windows at night.
• context Monitors or screens.
• context Very bright light from poorly positioned light fixtures.
• context Sunlight.

How do you detect glare?

There are several ways to find sources of glare.

• context When in your normal working position, look at a distant object at eye level. Block the light "path" from the fixtures with a book or cardboard. If the distant object is now easier to see, the light fixtures are probably producing glare.
• context To detect reflected glare, look at the task from your normal working position. Block the light falling on it from the front or above. If details are now easier to see, reflections are a problem.
• context Place a small mirror face up on the work surface. If the mirror reflects light from above, the light fixture is responsible for glare.
• context Look for shiny objects that reflect light. Glass in picture frames, glossy table tops, monitors or screens are common examples.
• context Ask workers if they experience sore or tired eyes, headaches or if they need to squint to see.

How do you correct glare problems?

To correct glare, try:

• context Using several small low-intensity light fixtures rather than one large high-intensity light fixture.
• context Using light fixtures that diffuse or concentrate light well. Indirect light fixtures or direct light fixtures with parabolic louvres are two possibilities.
• context Using indirect lighting or a combination of direct and indirect lighting.
• context Covering bare bulbs with louvres, lenses, or other devices to control light.
• context Increasing the brightness of the area around the glare source.
• context Using adjustable local lighting with brightness controls.
• context Positioning light fixtures to reduce reflected light that is directed toward the eyes.
• context Using low gloss paper or applying flat or semi-gloss paint and matte finishes on 'offending' surfaces.
• context Making sure there are no bright spots or light patterns that may bother the worker.
• context Removing highly polished and shiny objects.
• context Keeping general lighting levels at recommended levels.
• context Positioning the work station so that windows and fluorescent light tubes are parallel to the worker's line of sight.
• context Positioning the work station so that the light fixtures are NOT in the front or directly overhead.

How do you check and correct for poor contrast?

To correct for poor contrast:

• context Look for areas with great differences in light levels.
• context Look for objects that are hard to distinguish from the background.
• context Look for reading materials and monitors where it is hard to make out the print or characters from the background.
• context Increase the contrast between objects and the background. Use ink pens rather than pencils, and white paper rather than grey.
• context Adjust the monitor's brightness and contrast controls.
• context Decrease reflected glare. Use matte finishes on surfaces, and move or cover shiny objects.
• context Use contrasting colours for objects and the background. Paint stationary and moving machine parts in contrasting colours to improve visibility.

What should you know about poorly distributed light?

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:

• context Looking for dark areas and uneven lighting.
• context Using a light meter to check the illumination at various points throughout the workplace. With uniform general lighting, the minimum reading should not be less than two-thirds of the average value.
• context Supplementing or replacing light fixtures with ones that distribute some light upwards.
• context Painting ceiling and walls in light colours that reflect light.
• context Cleaning ceilings, walls and light fixtures.

How do you conduct a more detailed lighting survey?

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

• context 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

• context 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

• context 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

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: