Artificial lighting of museums and galleries is now largely fluorescent tubes, many of good colour-rendering properties, and cheaper to run than tungsten filament lamps. But although newer fluorescent tubes of recent introduction (triphosphors) have an even higher efficacy (light in lumens per unit quantity (watt) of electricity), their colour rendering is poor. The article explains the basic requirements, colour discrimination, metamerism, colour temperature, the two systems of calculating colour rendering (cie colour shift; crawford/npl spectral band). Unfortunately lamps with best colour rendering have not sold well, and philips 37 and 27 have been withdrawn. Economic pressures makes museums want high efficacy but until recently this meant poor colour. Now, however, lamps good from both points of view are available; their properties are tabulated, and recommendations given for museum and gallery basic requirements. Tables, figures, bibliography.