The effects of brightness-contrast are particularly striking when demonstrated by means of lighting, a simple apparatus being illustrated diagrammatically in Fig. 62. For example, if a hole _H_ is cut in an opaque white blotting paper and a large piece of the white blotting paper is placed at _C_, the eye when placed before the opening at the right will see the opening at _H_ filled with the background _C_. The hole _H_ may be cut in thin metal, painted a dull white, and may be of the shape of a star. This shape provides an intimacy between the hole and its environment which tends to augment the effects of contrasts. _R_ and _F_ are respectively the rear and front lamps. That is, the lamps _R_ illuminate _C_, which "fills" the hole and apparently is the hole; and the lamps _F_ illuminate the diffusing white environment _E_. The two sets of lamps may be controlled by separate rheostats, but if the latter are unavailable the lamps (several in each set) may be arranged so that by turning each one off or on, a range of contrasts in brightness between _E_ and _H_ (in reality _C_) may be obtained. (By using colored lamps and colored papers as discussed in Chapter IX the marvelous effects of color-contrast may be superposed upon those of brightness-contrast.) [Illustration: Fig. 62.--Simple apparatus for demonstrating the remarkable effects of contrasts in brightness and color.] If, for example, _C_ is very feebly illuminated and _E_ is very bright, _C_ will be pronounced black; but when the lamps _F_ are extinguished and no light is permitted to reach _E_, the contrast is reversed, and _C_ may actually appear "white." Of course, it is obvious that white and black are relative terms as encountered in such a case. In fact in brightness-contrasts relative and not absolute values of brightness are usually the more important. In order to minimize the stray light which emerges from _H_, it is well to paint the inside of both compartments black with the exception of sufficiently large areas of _C_ and _E_. The use of black velvet instead of black paint is sometimes advisable. It is also well to screen the lamps as suggested in the diagram. This simple apparatus will demonstrate some very striking effects of contrasts in brightness and will serve, also, to demonstrate even more interesting effects of contrasts in color.