PREVENTING SIGHT PROBLEMS: ABOUT LIGHT
All eyes need good light if they are to work well and without strain. This particularly applies to older eyes. A recent study of visual acuity in fifty-six old people (average age 76), both in their homes and in a controlled clinical setting, found that general levels of lighting were often so poor in the homes of elderly people that the number of people functioning as ‘blind’ was twice what it needed to be. Simply increasing the wattage of the lighting, they found, improved the vision of 82 per cent of the people. Don’t skimp on lighting. A 100-watt light bulb costs only pennies more a month to run than a 60-watt bulb.
As the eye ages, the lens becomes clouded and less pliable and the pupil decreases in size. Less light reaches the retina and near-focusing ability declines. Most people get glasses for their focusing problem but do little to increase the light that enters the eye. Research has found that the reduction of light reaching the retina is 50 per cent by the age of 50, and 66 per cent by age 60. Older eyes also react more slowly to changes in light levels, and because the cloudiness of the lens scatters light all around the inside of the eye, simply increasing the amount of light helps all this greatly. But this need for more light, especially at work, is not just confined to the old. Research shows that middle-aged workers need more light than do younger workers. An Ohio State University study found that 30-40-year-olds needed 17 per cent more contrast to see an object as clearly as 20-30-year-olds, and that those aged 60-70 needed two and a half times as much contrast to be able to see as well as the younger ones.
Older people, especially, are susceptible to glare and brightness. An older person facing a window all day at his or her desk is looking up at very bright light and then down at the work. This causes eye fatigue as the pupils enlarge and constrict. Also, when you look down with constricted pupils you will see very badly.
A way of seeing whether you are subjecting yourself to too much glare is to lay a mirror on your desk or table. If you can see a bright zone in the mirror when you are seated normally, it is a glare that could be causing you eye strain. Very highly-reflective surfaces can have the same effect too. Alter either the light or the furniture, whichever is easier, to overcome this problem.
When considering levels of illumination remember that intensity of light follows the inverse square law which means that moving a 25-watt bulb from 8 ft to 4 ft away is the equivalent of replacing it with a 100-watt bulb.
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