Health & Performance
Last Update: August 11, 2011
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Lighting & Human Health

Exposure to light – both daylight and electric light – can impact human health. These impacts are many and varied. For example, eyestrain can result from poor lighting where it is difficult to make out the necessary details; exposure to high light levels when trying to sleep can disrupt circadian rhythms; and certain wavelengths of light falling on the skin can produce either beneficial vitamin D or cause tissue damage. Lighting research has moved beyond just determining how much light is needed to see a person or an object to an examination of the lighting “dose” – the quantity of light that is helpful or harmful based upon the intensity of that light, its duration, its spectrum and even its timing (IESNA, 2008). There is still much to learn about the health effects of lighting but there can be no doubt that they need to be considered by the lighting designer.

Eyestrain
Eyestrain occurs when eyes become tired from intense and prolonged use such as reading fine print, viewing a computer screen or driving for long periods in poor-visibility conditions. Symptoms vary, but headache, blurry vision, dry or watery eyes, tense muscles and burning or itching eyes are often mentioned. Sleep or resting the eyes for a time usually alleviates the condition. While eyestrain can be annoying, it is rarely indicative of a serious eye problem.
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Flicker
Flickering light, the rapid and regular brightening or dimming of a light source, can simply be annoying or can be upsetting or can even cause physiological problems including epileptic seizures (Fisher et al, 2005). Any person who has experienced a strobe light-induced headache can attest to the power of flickering or flashing lights to cause disorientation or discomfort.
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Circadian System
Circadian rhythms are a basic part of life and can be found in virtually all plants and animals, including humans. The most obvious of these rhythms is the sleep / wake cycle but there are many others such as alertness, mood, memory recall and cognitive throughput. The human circadian system involves three basic components.
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Circadian Disruption & Health
Given that the circadian system is fundamental for much of human physiology, it should not be a surprise that when it fails or is disrupted for a long time, there are negative implications for human health. Further, given the role of the light / dark cycle in entraining the circadian system, it should not be a surprise that light exposure patterns have a positive role to play in the alleviation or prevention of health problems.
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Well Being
Circadian disruption occurs when people are exposed to light at a time when their circadian system expects darkness but even when this does not occur there is concern about how much light people are exposed to during the day. This concern arises because of evidence that exposure to light during the day affects well-being.
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Lighting For The Elderly
Lighting recommendations are typically written for the “average eye” i.e., the eyes of young adults who are in good health. Many eyes, however, are not average and there are populations of people who because of age, eye diseases, injury or other conditions that limit their vision have special lighting requirements.
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Health & Performance

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