The number of gas lights required to properly illuminate a room depends on its size, condition of wall surfaces, etc. The reflection from the walls in small rooms is proportionately greater than in large ones, and hence a less number of burners is required in proportion to the floor space. A 5' (cubic feet per hour) batswing burner is assumed to give a light of 16 candlepower under a pressure of .5 in. of water.

For large rooms, such as a church, etc., the proper illumination will be furnished by using one burner to each 40 sq. ft. of floor. If there are balconies, etc., extra lights must be provided according to the same rule. For smaller rooms, such as are found in ordinary dwellings, the proportion may be 1 light to about 80 sq. ft. of floor. The amount of light required is, therefore, from .4 to .2 candlepower per square foot, according to the size of the room.

If incandescent gas lights, such as the Welsbach, are used, the number of lights may be much less, as these lights furnish from 50 to 60 candlepower on a consumption of about 3 cu. ft. of gas per hour, at a pressure of .5 in.