Experiments done in 1973-74 attempted to classify paintings into groups corresponding to best illuminating light sources (tungsten or daylight) for them. Projected experiments will try to determine a light source with the least harmful effects and optimum color rendering. The overall tone of the picture is the basis for assigning a particular light source. Influences of epoch, country, and genre are also being studied. Conclusions: the warmer the color of the picture, the lower the color temperature must be; 3000 degrees K -- 4800 degrees K is the correct temperature range for light sources.