Thought Bytes...
August 2003

Is brighter better?

As we get older, our eyes are changing. Not only do your arms seem shorter, but it seems that we need more contrast to focus. Natural age related changes in the lens and muscles controlling the lens make it harder to focus on material in what used to be a comfortable reading range. This is compounded by the increased sensitivity to glare and slight yellowing of the lens, making the world slightly greyer.

When we read printed material, light is reflected off the page onto the retina at the back of the eye. There it is transformed into neural impulses that are sent to the brain and appropriately interpreted. When written materials seem dull, the natural tendency is to add more light. This increases the amount of contrast between the dark characters and the lighter background.

Adding more light to written material is fine, provided that the reader cannot see the actual light source. Seeing a light source is called direct glare. We have all had the experience of seeing spots after a flash bulb is used to take a picture. That is direct glare taken to an extreme. More commonly though, is seeing a light fixture or light bulb in the peripheral vision. Although you are not looking at it directly, the image of the light is still collected by the retina.

The natural tendency is to look away from bright light sources. When you can see a light source, you tend to tilt your head down slightly or furrow your eyebrows in an effort to shade the eyes. At the extreme, workers may wear hats or visors to decrease the amount of light entering the eye. Many workers are unaware of the eye strain associated with direct glare and unconsciously change their posture to compensate. Leaning forward or to the side are the most common postural adjustments.

The solution is to make sure that the light source itself cannot be seen in the peripheral vision. This could mean turning out an overhead light or re-positioning a task lamp.

Reading from computer screens presents another dilemma. Computer screens produce light. In this case, the image is collected by the retina directly from the light source. Adding light to a computer screen produces reflected glare. You know you have reflected glare if you turn off the screen and see light fixtures or objects reflected on the screen.

Reflected glare causes people to shift their posture too. I have seen many workers move their torso and head from side to side to create a shadow on the screen that they can see the text through. Sometimes the monitor will be turned slightly to one side to compensate for a light source from the side.

The most common source of reflected glare however is from overhead lights. Often in an effort to raise the screen, workers will simple angle it up. This allows light to reflect off the screen into the users eyes – reflected glare. For this reason, the monitor screen should be perpendicular to the desk. Remember, the only reason that papers are sloped is to optimize the amount of light reflected off them. Because computer screens produce light, we don’t need an angle to them.

The other issue around computer screens is the amount of light surrounding them. When the area around the screen is brighter than the screen, the receptors in the eye are not being optimally used. The centre of the eye (where the cones are) is designed to work in brighter light. The peripheral area of the retina (where the rods are) is designed to perceive motion in relatively dark environments.

If the screen is darker than the window behind it, then the eye must continually adapt to the conflicting use of the receptors. This makes people lean in toward the screen in an effort to decrease the amount of peripheral light entering the eye – increasing strain to the lower and upper back, neck and shoulders. Although you may enjoy the distraction of being able to look out the window, closing the blinds behind the monitor will definitely help your posture and eye comfort.

Is brighter better? It may seem like I am suggesting working in a cave. Well, working with computer does mean that we need less ambient light. Most offices are considerably over-lit for computer users. I usually suggest decreasing the light level by about ¼ to 1/3 by turning out selected bulbs or fixtures. Test of direct glare by wearing a hat or visor at the computer for a few days. Because reading from paper needs more light than computer work, task lamps can be used to brighten up printed materials. The key is to illuminate the task, not the eye.

Feedback

Dear Sharon,

I want to congratulate you on the fine work you are doing on the Working Well project and in particular on the August piece on lighting in the workplace. It was well researched and well written. I agree with your suggestion of reducing the number of fixtures or tubes, etc. Many offices are over-lit by a good 50%. I often advise my patients who report eye fatigue on the job to try removing half the fluorescent tubes from the overhead fixtures and adding a specific task light. As you point out, location of the light source relative to the task is at least as important to visual comfort and efficiency as is the quantity of light in the room.

Good work.

Scott D. Brisbin O.D., F.A.A.O
Optometrist

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