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Impact of Light on Human Beings

Light and dark, hot and cold or the cyclical change of the seasons: the rotation and inclination of the Earth give rise to constantly recurring changes that, in the course of evolution, have resulted in hu-man beings developing a circadian system – a system of internal clocks that anticipate such changes. Like the complex movement of a clock, it controls and coordinates the 24-hour variation of all bodily functions. Disrupting it can have a variety of negative effects, producing symptoms of disorders such as depression or immune disease.

Scientists have been studying the biological impacts of light perceived by the human eye since as long ago as the 1980s. But it was not until 2002 that they discovered ganglion cells in the retina of mammals that are not used for “seeing”. The newly identified cells respond most sensitively to visible blue light and set the “master clock” that synchronises the system of internal clocks with the external cycle of day and night.

This booklet provides a practical and user-oriented summary of what science knows today about the non-visual impact of light on human beings. It is not a final, authoritative work but an ambitious at-tempt to describe the nascent, fast-growing field of research examining light, health and efficiency.


Human evolution is shaped by light

Biological rhythms

Our internal clock

Biologically effective light

Biologically effective light indoors

Light therapy

Lighting design

Lighting quality and energy efficiency

Practical example: Dynamic office lighting

Practical example: Dynamic industrial workplace lighting

Practical example: Dynamic school lighting

Practical example: Dynamic retirement home lighting

Practical example: Dynamic domestic lighting

Lamp spectra


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