Eyesight Essentials, Melbourne
Lighting is essential for our daily activities and is of particular importance to people with a vision impairment. Vision-impaired people often require two to three times the amount of light a sighted person needs.
Ocular condition, level of vision, age and pupil size of the person need to be considered, as well as the type and amount of lighting. There is great variation in the lighting needs of people with vision impairment; their preferences and performance should be evaluated on a case-by-case basis.
Lighting to assist people with vision deficiencies can be natural or artificial. There is a large variety of artificial sources of light. The type of lighting, light output, the location of the light source and the specific task for which it is intended all have a major influence on functionality and efficiency.
While the wattage of the light source is important, the inverse square law of illumination tells us that the position of the light source is more important. Illuminance is the amount of light falling on an object or surface, measured in lux. In accordance with the inverse square law of illumination, positioning the light source closer to the surface of the task increases the illuminance (Figure 1). For example, halving the source to surface distance will quadruple the illuminance.
When the light source is not perpendicular to the task surface, the cosine law of illumination applies and the illuminance is reduced. In most cases, the light source should be directed over the shoulder of the stronger eye and held close to the reading material to get maximum illumination.1
Types of lighting
This light can be beneficial but consideration needs to be given to the possibility of glare issues. Suggestions for patients include:
- Keep windows clean
- Tinting of windows/blinds/curtains can be helpful
- Work with his or her back to a window.
Select the appropriate type of light for the task
- General: lighting necessary for moving about a room, minor visual tasks
- Direct: directed to work area efficiently with low light loss, for example, down-lights
- Semi-direct: 60-90 per cent of light emitted is directed to work area, for example, surface fluorescent
- Indirect: reflected from ceiling and walls (poor efficiency) for example, pelmet lighting
- Diffuse: light diffused with soft shadows for example, opal glass or a sphere pendant
- Task: high level of illumination required for specific tasks.
Colour temperature of light
Single globes or tubes are available for light fittings in `warm white', `cool white' or `daylight'.
- Warm white: 2800-3000 Kelvin (accentuating longer wavelengths; yellowish to reddish white in appearance)
- Cool White: 4000-4500 Kelvin (accentuating shorter wavelengths; bluish white in appearance)
- Daylight: 6500 Kelvin (full spectrum).
What lighting is beneficial for low vision?
- Even illumination throughout the general environment ensures a reduction in distracting shadows. Full spectrum fluorescent lighting serves this purpose well.
- Lights should be covered by a diffuser to minimise glare and reduce reflections.
- Light colours are preferable for ceiling and walls. Light switches should be situated at a standard height, in a suitable location and in a colour that stands in contrast to the surrounding area.
- The patient should not be positioned facing a light source. Focal light shining from behind is best.
- Task lighting should be used in conjunction with general room lighting for safety reasons. When the patient moves away from the task location, the general area should still be illuminated.
- Task lamps should have a wide shade surrounding the globe, the globe should be recessed, and have an adjustable arm to change angle of tilt (about 45 degrees) and so that it can be positioned close to the task to maximise illuminance.
- For safety reasons, the patient should be instructed not to use a globe that is higher than the recommended wattage.
- If a lamp and magnifier are separate entities, the lamp should be placed close to magnifier, so the light is shining under the magnifier on to task area.
- When prescribing magnification, consider the need for an illuminated magnifier and its colour temperature.
Table 1 indicates the various aspects of artificial light. Both fluorescent and compact fluorescent lamps (CFL) offer better options for a patient with vision impairment.
Where to obtain lighting products
Officeworks and specialised lighting shops like Beacon sell a combined low-powered magnifier and lamp. The cost varies between $50 and $80. The specialised lighting shops have the benefit of allowing the client to try before they buy. The same applies to globes with different colour temperatures; the customer may have a demonstration to find out which light is the most suitable.
Quantum, Pacific Vision, Royal Society for the Blind, Vision Australia and European Eyewear all have a range of portable, compact, clamp style and standard lamps with a range of prices from $45 to $350. A variety of illuminated magnifiers of different strengths and colour temperature is also available.
Rooms and task areas in the home
A home lighting assessment may be beneficial to the patient, to see if the present lighting is adequate. An orthoptist or service provider who specialises in low vision can do this (Tables 2 and 3).
Lighting can have a considerable impact on activities of daily living, and in particular reading, for your patients with vision impairment. Lighting is a commodity that can be easily overlooked, but it is a simple and effective management strategy that you can suggest to your patients with low vision.
For further information, visit www.eyesightessentials.com.
1. Williams DR. Nonoptical and accessory devices. In: Brilliant RL. Essentials of Low Vision Practice. Boston: Butterworth-Heinemann; 1999.
2. Australian/New Zealand Standard. Interior and Workplace Lighting. Part 1: General Principles and Recommendations. AS/NSZ 1680.1. Sydney, NSW; Standards Australia/Standards New Zealand: 2006.