This section is from the book "A Treatise On Architecture And Building Construction Vol4: Plumbing And Gas-Fitting, Heating And Ventilation, Painting And Decorating, Estimating And Calculating Quantities", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
254. Rooms having dark-colored walls, or having much colored drapery, will require more light than they would if finished in white. The white walls reflect and disperse the light, thus aiding the general illumination, while colored walls reflect less in proportion to the brightness of their coloring.
The rule commonly used for computing the number of ordinary 5-foot Batswing burners which will be required to properly illuminate a church or other large room is as follows:
Divide the area of the floor of the room by 40; the quotient will be the number of burners required.
If there are balconies, etc. extra lights must be provided for them by the same rule. The divisor given may be varied from 40 to 80 to suit smaller rooms, such as are found in ordinary dwellings. The reflection from the walls is proportionally greater in small rooms; therefore, a less number of burners is required in proportion to the actual floor space.
How many 5-foot Batswing burners will be required to properly illuminate a church having an auditorium 70 ft. X 100 ft., and a balcony having 2,000 square feet floor area?
The main floor will require 70 x 100 /40 = 175 burners, and the balcony will require 2000/40 = 50 burners; 175 + 50 = 225 burners.
Ans. One 5-foot burner is assumed to give a light of 16 candle-power. The amount of light required is, therefore, 16 candlepower to a floor space of 40 square feet in large rooms, to 80 in small ones, or .4 to .2 candlepower per square foot of floor space.