2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/13132I present here a review of the observed characteristics of the optical diffuse light in clusters, the possible sources of this light and some of the theories that try to explain the existence of big envelopes around the brightest cluster galaxies.To appear in "IAU Coll 171: The Low Surface Brightness Universe", held July 1998, A.S.P. Conference Series, 7 pages, LaTex, requires paspconf.styAstrophysicstext