Illumination.
—The development of high-efficiency lamps has caused a radical change in the methods of illumination. With cheaper light came the desire to more nearly approximate the effect of daylight in illumination. This has brought into use indirect illumination, in which the light from the lamp is diffused by reflection from the ceiling and walls of the room. Illuminating engineering is now a business that has to do with placing of lamps to the greatest advantage in lighting any desired space. In large and complicated schemes of lighting professional services are necessary, but in household lighting the required number of lamps for the various apartments are almost self-evident. The lighting of large rooms, however, requires thoughtful consideration and in many cases the only definite solution of the problem is that of calculation.