A mild, subdued light aids the hypnotic influence, while a strong and bright light is a pronounced hindrance. Red and yellow are especially unfavorable colors and such globes or lamp shades should not be used, for they give a glare to everything in the room and tire the eyes. Such lights in a room make ordinary sleeping difficult and their effect in delaying the securement of hypnotic sleep will be found very noticeable.

A soft, blue light will aid the operator. It rests the eyes and consequently rests the brain, and more than any other light, it favors sleep. Do not use a dark blue shade, for that would attract attention by its peculiarity. If blue is not obtainable, a pale green may be used. Of course, the subject is not to look directly at the light; he is simply to realize the benefit of the diffused, soft tone cast about the room.

Bright sunlight should not be admitted. In the daytime a room with north windows is best, and cloudy days are more favorable than bright ones. When shades are used, blue or green are to be preferred. Always allow plenty of light in the room, so that the subject need not make an effort to look at objects to which you call his attention. But never admit a strong light.