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reproduction of colour or the selection of colours are the elements that determine colour climate
and visual comfort.

The prerequisites that an illumination system must fulfill in order to provide
the conditions necessary for visual comfort are the following:
1) uniform illumination;
2) optimal luminance;
3) no glare;

4) adequate contrast conditions;

5) correct colours;

6) absence of stroboscopic effect or intermittent light.

It is important to consider light in the workplace not only by quantitative
criteria but also by qualitative criteria.
The first step is to study the work station, the precision required of the tasks
performed, the amount of work, the mobility of the worker and so on. The light
should include components both of diffuse and of direct radiation. The result of the
combination will produce shadows of greater or lesser intensity that will allow the
worker to perceive the form and position of objects at the work station. Annoying
reflections, which make it harder to perceive details, should be eliminated, as well as
excessive glare or deep shadows.

The periodic maintenance of the lighting installation is very important.
The goal is to prevent the aging of lamps and the accumulation of dust on the
luminaries that will result in a constant loss of light. For this reason, it is important to
select lamps and systems that are easy to maintain. An incandescent light bulb
maintains its efficiency until the moments before failure, but this is not the case with
fluorescent tubes, which may lower their output down to 75% after a thousand hours
of use.

9.3 Basic Light Engineering Notions

The illumination of industrial buildings is characterized by quantitative and
qualitative parameters (Figure 9.1).
Light flux (F) is the intensity of light that is evaluated by human eyesight in
accordance with light sensation. The unit of light flux measurement is lumen (lm).
Light intensity (I) is a magnitude defined by the ratio between light flux (F)
and solid angle (W) within which light flux is equally allocated:

I=F/W.
The unit of light intensity measurement is candela (cd).

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