At nightfall, the general feeling is that the more light, the better. More road safety, more tranquillity for the citizen and more beautiful are the important buildings. But in this race to illuminate more and more, one loses, among other things, the possibility of contemplating the landscape of the night sky, declared by UNESCO to be the heritage of future generations.

The Instituto de Astrofísica de Canarias (IAC) knows this well, and in order to guarantee research activity and, in particular, to preserve the astronomical quality of its observatories, on 31 October 1988 the Spanish Parliament approved the Law on the Protection of Astronomical Quality of the IAC Observatories.