The art museum affords a multitude of opportunities for utilizing the expressiveness of light. This is more generally true of sculptured objects than of paintings because the latter may be treated as a whole. The artist almost invariably paints a picture by daylight and unless it is illuminated by daylight it is altered in appearance, that is, it becomes another picture. The great difference in the appearance of a painting under daylight and ordinary artificial light is quite startling, when demonstrated by means of apparatus in which the two effects may be rapidly alternated. Art museums are supposed to exhibit the works of artists and, therefore, no changes in these works should be tolerated if they can be avoided. The modern artificial-daylight lamps make it possible to illuminate galleries with light at night which approximates daylight. A further advantage of artificial light is that it may be easily controlled and a more satisfactory lighting may be obtained than with natural light. Considering the cost of daylight in museums and its disadvantages it appears possible that artificial daylight with its advantages may replace it eventually in the large galleries. If the works of artists are really prized for their appearance, the lighting of them is very important. Sculpture is modeled by light and although it is impossible to ascertain the lighting under which the sculptor viewed his completed work with pride and satisfaction, it is possible to give the best consideration to its lighting in its final place of exhibition. The appearance of a sculpture depends upon the dominant direction of the light, the solid-angle subtended by the light-source (skylight, area of sky, etc.) and the amount of scattered light. The direction of dominant light determines the general direction of the shadows; the solid-angle of the light-source affects the character of the edges of the shadows; and the scattered light accounts for the brightness of the shadows. It should be obvious that variations of these factors affect the appearance or expression of three-dimensional objects. Therefore the position of a sculptured object with respect to the window or other skylight and the amount of light reflected from the surroundings are important. Visits to art museums with these factors in mind reveal a gross neglect in the lighting of objects of art which are supposed to appeal by virtue of their appearances, for they can arouse the emotions only through the doorway of vision.