GENERATION OF LIGHT

Generation of Light

Generation of Light

Q1- How light is generated in incandescent lamps?

Ans. There are a number of ways of calculating the theoretical number of lumens that could be obtained by the perfect conversion of a watt of electricity into light. One such calculation puts the amount at 673 lumens per watt. Other calculations go as high as 692 lm/watt. (Note that the energy in a lumen is dependent on the wave length of the light being examined.) Whatever the figure, it dwarfs the best of incandescent lamps which produce less than thirty lumens of visible light per watt. Outside of the theatre, modern energy saving approaches to lighting have resulted in tremendous savings in energy costs and effect on the environment.

The stage, however, lags far behind, mostly because it remains committed to the concentrated filament incandescent lamp which is easy and safe to use and can be dimmed by relatively simple electronic equipment with only minor color shift problems. Also the theatre has a huge investment in equipment designed around the incandescent lamp. The incandescent lamp's inefficiency, which results in most of the energy it consumes being converted into heat, costs the theatre double; once for the power to operate the lamps and again for the extra air conditioning needed to remove the excess heat from the building. The heat also is destructive to color media and equipment. Additionally, it is a constant annoyance to actors, singers and anyone on stage.

The incandescent lamp is a very poor source of cool colors, particularly pure blue. This increases lamp and power costs because much more power is needed to produce usable quantities of blue light. Moreover, while the concentrated filament is a reasonably small source, it is still far from a theoretical point, particularly in large wattage lamps which must have larger filaments. This makes collection of its light difficult and inefficient. It has long been known that any gas which is ionized by electrical current, will emit radiant energy, usually much of it in the visible range. This phenomenon is found in nature in the northern lights and can be easily reproduced on a small scale by enclosing any gas or combination of gases in a glass tube equipped with electrodes and applying sufficient voltage to cause current to flow through the gas.

The result will be a glow of wave length(s) typical for the gas(es) used. A spectroanalysis of this light will reveal that it is made up of narrow lines representing individual or closely spaced groups of wavelengths with darkness between—a line spectrum. The practical requirements for making light by gaseous discharge are quite different from those for operating an incandescent lamp. First, the gas must be completely enclosed in the tube, not polluted by air or any other unintended gases. Electrodes must be installed at the ends of the tube and carefully sealed to prevent either the escape of the interior gas or the intrusion of air. If the gas is at relatively low pressure ...