The effects of lighting extend further than visual effects only.  Relatively recent medical and biological research has shown that lighting entering the human eyes has also important non-visual biological effects affecting our health and well-being.

For more than 10 years, Wout van Bommel has been involved in this subject. He was responsible for two international expert symposia (Vienna 2004, Ottawa 2006) where medical, biological and lighting experts set the way for putting the new knowledge into practical use. He was chairman and is Board member of the Dutch "Light & health Research" Foundation.

The non-visual influence of light works via the control of the biological clock in the brain. The biological clock (2) has a nerve connection (blue) with light sensitive cells in the eye (1) and with the pineal gland (3). The pineal gland controls the production and suppression of various hormones. Two of these hormones, cortisol (that gives us energy) and melatonine (that makes us sleepy) regulate our sleep-alertness rhythm.
The American David Berson made in 2002 the sensational discovery of a new type of light sensitive cell in the eye. It are especially these type of cells that determine the  biological effects and not the well known cones and rods that we use for vision. These "noval" cells are far more sensitive for blue light than the cones and rods are.

Healthy lighting therefore is not only dependent on the level of light but also on the colour tint of light. When daylight is not sufficiently available in a building the artificial lighting should  take care that people still benefit from the natural effects of light. Only the last few years a wealth of new information has been collected by lighting professionals. This not only relates to work during daytime but also to shift work with night shifts.
In the meantime we have also learned that lighting sometimes can be used as a therapy for certain diseases. Examples of diseases where lighting therapy can have positive effects include: decreased sleep quality in elderly, irregular wake-sleep rhythm in Alzheimer patients, seasonal affective disorders (SAD also called winter depressions) and geriatric depressions. Special lighting in homes for elderly and homes for demented people is therefore more and more applied.