Just as the eye, little by little, adapts to a certain level of light, perceptions of colour also evolve gradually. This is how a dominant purplish-pink tone, which is overwhelming and awkward at the start of the light emission, rapidly becomes blurred with chromatic adaptation. In particular, this faculty makes it possible to consider as white a truly white surface which at first appeared purplish-pink. Obviously, photography does not benefit from this adaptation. In these conditions, the 80 B filter offers two possible appropriate corrections:
• On the lens (disadvantage: implies a correction of exposure);
• On the lens of the projector (correction during slide projections).
With digital photos, the correction is made automatically. The red paint revealed by the lighting is efficiently restored, whereas the (purplish-pink) luminous pollution is eliminated. As a general rule, with the fluorescent tube, it is impossible to pass in front of the tiniest bit of red colour without seeing it. Hence, a very small coloured element that was previously glimpsed and not recorded suddenly commands attention.
It comes to light by springing out of the wall, whereas it has perhaps already been forgotten because it was not noted down previously as soon as it was seen. As is evident, this lighting can usefully be added to the array of methods of studying decorated caves. The heat emission produced by the tube is very low. The stability of the fragile environment is safeguarded by spacing out the work sessions.4
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