Light and Illumination

Compared with other branches of engineering, as the transformation of electrical power into mechanical power in the electric motor, or the transformation of chemical into mechanical energy in the steam engine, we are at a disadvantage when dealing with light and illumination, because we have not to do strictly with a problem of physics, but are on the borderland between applied physics, that is, engineering and physiology. Light is not a physical quantity, but is the physiological effect exerted on the human eye by certain radiations.