Natural and Artificial Light
As light enters the eyes, conveying images to be registered by the brain, it also affects the pineal and pituitary glands - the master controllers of the endocrine system. Any change in endocrine balance will cause major alterations in body chemistry and physiology and will affect both health and behavior.
Experimentation with animals is showing us the relationship between the presence or absence of light and hormone secretion in the body. A Wisconsin research team found that they could increase both weight and milk yield in cattle by 10 to 15 percent simply by increasing the number of hours of light the animals received. The normal nine to twelve hours of light exposure was raised to sixteen hours per day. No additional consumption of food was necessary to accomplish these gains. The entire effect seems to be the result of the manipulation of the light.*
Industrialized egg farming has relied on the same techniques for years. Confined to their cages inside large, light-controlled buildings, the chickens readjusted to a rhythm motivated by the increased light. The result was increased production of eggs (although quality may be adversely affected).
* Peters, R. R., et al., "Supplemental Lighting Stimulates Growth and Lactation in Cattle," Science,
Vol. 99 (February 24, 1978): 911-12.