July 6, 2013

Lighting For Low Vision

Posted in: Daily Living

by Dan Roberts
with supporting information provided by
Roy Cole, O.D.

What is the best kind of lighting for visually-impaired people? Is one kind of lamp better than another? These are two of the most-asked questions in a subject field that can be confusing at best.

The bottom line is that people should use the lighting that works well for them. To help with that decision, here is some basic information about what is available.

Types of Lighting

Full Spectrum. The closest to actual sunlight, covering the entire range of colors. Drawbacks are that they do not include ultraviolet (UV) light filters, and they are very high in the blue light spectrum. Blue light is responsible for glare, and some studies have shown that it, like UV rays, may also be harmful to the retina. For more on this subject, see “Blue Light and Macular Degeneration” and “Artificial Lighting and the Blue Light Hazard“.

Incandescent. Commonly used in the form of a light bulb in table or desk lamps, this is the safest light source for the eyes. It is not, however, the most economical, nor is it good for contrast or accurate color perception.

Tungsten-halogen (or simply “halogen”). The brightest and whitest light, which is excellent for enhancing contrast. Good for use where a lot of light is desired, but the heat intensity of the lamp can be a problem. It is especially good for overhead track lighting.

Fluorescent. Bright and economical, this type of lighting is seen most often in public places. Modern fluorescent tube lamps and “compact fluorescents” are of the “warm white” variety, so they are bright and safe.

Light Emitting Diodes (LEDs). Efficient, durable and small. Initially more expensive, but much longer lasting and cheaper to run than other light sources. The wider, brighter, and closer the field of light, the more potential risk it carries for the retina. A small array of white LEDs in a task lamp would provide good, safe lighting.

Roy Cole, O.D. (Director of Vision Program Development, Jewish Guild HealthCare) offers the following suggestions for choosing the best lighting.

For task lighting, the lamp (bulb) should be in an adjustable fixture, and the distance of the light source from the page is as important as wattage. The further away the lamp, the less illumination on the page, and the closer, the more illumination. In fact, if you double the distance, you need a bulb 4X as strong to keep the same brightness on the page. Triple the distance, and you will need 9X as strong a bulb, etc. This is referred to as the “inverse distance squared rule.” So adjust the distance of the bulb for optimal visibility.

To reduce the heat of the bulb, use a lamp with an internal reflector (a double shade). This reduces the heat significantly, and allows you to have the lamp closer to the face than you would with a single shade (especially one made of metal).

Here are some other guidelines from Dr. Cole:

If one eye is better and used for reading, position the lamp on that side of the body, slightly to the side. What you don’t want is the light reflecting from the page into your eyes. To check this, turn the light off, place a mirror on the page being read, and see if the lamp appears in the mirror. If it does, re-position it. It should still be close to the page, and to the side of your face, but now perhaps at a slightly greater angle. (Of course, too much of an angle will also reduce the brightness on the page, so you have to find the optimal position for you.) You also want to adjust the light so there are no shadows on the page.

A typoscope is a black card with a slot cut in it to expose the line being read as you move it down the page. This will help to reduce the glare reflecting off the page and improve the apparent contrast of the print.

If you have a room with fluorescent lighting, adding incandescent or halogen task lighting may help to make it more comfortable.

Glare

Glare from reflective surfaces can be a hindrance for people whose eyes are not capable of modulating light, due to retinal disease. Blue blocker glasses can help by cutting down the haze which surrounds bright objects (caused by blue light waves, which are very short and easily scattered.) Polarized sunglasses will help to reduce glare, especially if the light is reflecting off of a flat surface that is in front of the viewer (eg. a body of water, snow, or a wet road.) The reason for this is that light reflected at a particular angle is “plane polarized” (in the horizontal direction). Polarized lenses transmit light only in the vertical direction, thus removing the reflected horizontal light. Blue blocker lenses and polarized sunglasses may be purchased commercially, or optometrists can add blue-blocking tint or polarization filters to prescription lenses.

Suggestions for Better Lighting

Finally, here are some additional suggestions for improving lighting in the home and workplace:

  • Place the light directly where you need it. Swivel lamps are preferable, as they can be raised or lowered in order to direct the light.
  • Aim the light directly on the task at hand.
  • Install dimmer switches for controlling the amount of light in the room.
  • Install under-cabinet lighting for tasks in the kitchen or work areas.
  • Install extra lighting in places where it may be difficult to move around, such as hallways and stairs.
  • Install light switches in accessible locations.
  • Install switch plates that are lighted or contrast with wall color.
  • Install preset light timers in difficult areas.
  • Watch television in a lighted room. It is easier on the eyes. Be sure, however, that the light isn’t placed where it will cause glare or reflection off of the screen. This can be easily checked with the television screen dark.

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