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  Light is
made up of electromagnetic radiations of wave length between 380 and 780
nm.
The different chromatic sensations occur according to the wave length,
from violet (400nm) to red (700nm) passing through green blue (500nm) and
orange yellow (600nm).
Light is white when all the spectrum wave lengths are present; on the
contrary light shows different colours and tones when some wave lengths
prevail.
The greatest sensibility of the human eye is around 500-550 nm and it can
vary, although very little, on the basis of the intensity of the
radiation of light.
The most important characteristics of light are:
- The flux of light, i.e. the power given out by a source or received by
a surface. It is measured in lumen, i.e. the quantity of light energy
given out by a source in the unit of time.
- The intensity of light, i.e. the flux of light of a source in one
specific direction. It is expressed in candles.
- The illuminance, i.e. the flux of light that reaches a unit of area. It
is expressed in lux (lumen/m).
An incorrect lighting of the working places is certainly an important
source of physical and psychological distress and may cause problems in
the acceptance and quality of work. However it does not cause visual
alterations.
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