Most natural light comes from the sun, including moonlight. Its origin makes it completely clean, and it consumes no natural resources. But man-made sources generally require consumption of resources, such as fossil fuels, to convert stored energy into light energy. Electric lighting is superior to flame sources because the combustion of wood, gas, and oil produces pollution within the
space being illuminated. Moreover, electricity can be generated from natural, nondepletable sources of energy, including the energy generated by wind, hydro, geothermal, and solar sources
How an electric lamp operates determines virtually everything about the light created by it. The common incandescent lamp generates light through the principle of incandescence, in which a metal is heated until it glows. Most other lamps, however, generate light by means of a complex chemical system in which electric energy is turned into light energy where heat is a side effect.
These processes are usually much more efficient than incandescence—at the cost of complexity and other limitations. For instance, a fluorescent lamp generates light by a discharge of energy into a gas, which in turn emits ultraviolet radiation, which is finally converted to visible light by minerals that “fluoresce.” This process generates light about 400 percent more efficiently than incandescence
and is the reason fluorescent lamps are promoted as environmentally friendly.