"Let there be Light!" declared God at the original act of creation, for indeed - together with water, food and oxygen - light is essential for human survival. Like the flowers that close their petals at the end of the day, humans too start to shut down when deprived of full spectrum light for extended periods of time. Wendy Champagne investigates.

Every year with the approach of winter and the decrease in daylight hours, thousands of people across the planet develop symptoms of a depression known as "Seasonal Affective Disorder" or SAD.

Each of us has experienced mid-winter blues to some degree. When you leave for work before sunrise and walk out of the office at 5 0'clock in the afternoon and it's already dark, you can quite suddenly feel depressed; it's as if the day's been stolen from you.

SAD seriously affects about two percent of people in Northern Europe and America, with a further ten percent experiencing milder symptoms. Women are four times as likely as men to suffer from SAD, and across the world the incidence increases with distance from the equator; except in snow-covered areas where the snow acts as a giant reflector for the available light.

"I find it almost impossible to pull myself out of bed in winter," says Suzie Smith an Australian now living in Aberdeen, Scotland. "During the first winter up here I began craving food, especially potatoes and pasta. I was irritable, anxious, tired all the time and I had a constant cold." All classic symptoms of SAD, which also include lowered resistance to infection, despair, joint pain, lethargy and hopelessness.

"People who have SAD are more sensitive to light," says Dr Bobbi Clarke, a US doctor specialising in SAD. And the only real cure for light deprivation is light therapy. This therapy can come in the form of extended periods in sunlight, taking extended trips to the snow, or sitting in front of a "light box'.

Light nutrition

Rays from sunlight, enter the eyes and stimulate the pineal gland and pituitary glands, which have a major role in controlling the entire endocrine system, and triggering hormones. Vitamin D is synthesised by ultraviolet in the skin and Vitamin D receptors help proper bone development and facilitate the absorption of calcium.

Under natural light or an artificial source that duplicates natural light, studies show there is less human fatigue and stress and better visual acuity and production. But according to pioneer light scientist John Ott, tinted sunglasses, incandescent bulbs and most fluorescent lights can actually interfere with our health.

John Ott has been warning against the unhealthy affects of some kinds of light for the last thirty years, yet only recently have scientists produced basic research to support his ideas.

Certain scientists refer to full-spectrum light - the light from sunlight or fluorescent bulbs specially designed to simulate sunlight - as a "super-nutrient". Full-spectrum light is used to treat SAD, psoriasis, neo-natal jaundice; it's used in dairies to stimulate milk production, and in nurseries to control the flowering of plants to preset schedules.

The Syracuse zoo in New York reported an upsurge in procreation when they installed sunlight-stimulating lights in an effort to curtail vandalism. And one recent study found calcium absorption dropped off in elderly people sitting indoors under incandescent lighting, whereas it increased in those sitting under full-spectrum lighting.

Professor John Ott believes fluorescent light - used in 98 percent of all Australian office buildings - is the most "nutrient-deficient of all lighting devices. Concern for workers health in Germany lead that government to restrict its use in public buildings. While in Russia, an "enlightened" understanding of the benefits of full-spectrum lighting on performance and health, mandates its use in the workplace.

Even the colour tint of your sunglasses can rob you of light nutrition by preventing certain light wavelengths from entering your system, according to John Ott, who persuaded a man with prostate cancer to stop wearing pink-tinted sunglasses and claims he affected a cure.

Light cures. In its full spectrum, light can hasten the healing process, relieve depression, balance the hormones, and generally make you feel good.