How much light do we need?
August 6, 2012 3 Comments
As electric lighting developed, recommended light levels were raised. This was due to; in part, increased luminous efficacy of lamps, overall national prosperity and the availability of relatively cheap electricity. However, with the oil crisis in the 1970s energy costs suddenly rose steeply and lighting levels became static and are basically the same today.
More recently, many common visual tasks have been made easier by the introduction of electronic visual displays replacing printing and handwriting and many office occupants are satisfied with lighting levels less than the recommended 500 lux.
In future should lighting levels be based, not simply on visual efficiency, but on requirements of good health? Electric lighting originally supplemented daylight but now we are totally dependent upon it and people are rarely reliant on daylight alone whilst indoors. Deep plan offices and shopping malls are illuminated all the time regardless of the amount of daylight available. Traditional outdoor sports are now played in enclosed stadia and at night. Even our cars have tinted windows to reduce the amount of daylight. Lifestyles today spend less time outdoors. A lunchtime kick-about outdoors in the car park is more likely to be a sandwich at your desk these days.
Seasonal affective disorder (SAD) was identified in the 1980s and is considered to be because of the lesser amount of daylight during the winter months (for northern hemisphere). Treatments suggested include exposure to 10,000 lux of white light for at least one hour a day, although more recently 300 lux of green light is considered to be equally effective.
I can remember my grandfather suggesting that time should be found to view the distant green hills, and he offered two reasons. To focus at ‘infinity’ relaxed the eye muscles, and green was a restful colour in the middle of the visual spectrum. He was a countryman at heart and I suspect it also gave him a chance to dream.
Introducing more daylight in our lives must be a benefit. We just don’t know how to quantify its value.