6 pages, 4 figures, 2 tables, 28 references. We thank the Scientific and Technical Services of the University of Barcelona for their excellent technical assistance with the CSLM and the Department of Fluid Mechanics Energy Engineering at the Superior School of Engineering of the University of Seville for their assistance with the spectral measurements of light sources.Artificial illumination can harm works of art by inducing the development of photosynthetic biofilms. With the aim of preventing biodeterioration or esthetic damage to such surfaces, we evaluated and compared the effects of illuminating biofilms formed by Gloeothece membranacea (cyanobacteria) and Chlorella sorokiniana (Chlorophyta) using exclusively white or green light.This work was supported by the EU Programme for Energy, Environment, and Sustainable Development in the CATS Project, contract EVK4-CT-2000-00028.Peer reviewed