If an ordinary tungsten-lamp bulb be filled with an inert gas such as nitrogen, the filament may be operated at a very much higher temperature without any more deterioration than takes place in a vacuum at a lower temperature.  This gives a more efficient light but a less efficient lamp.  The greater output of light is compensated by losses by conduction of heat through the gas.  In other words, a great deal more energy is required by the filament in order to remain at a given temperature in a gas than in a vacuum.  However, elaborate studies of the dependence of heat-losses upon the size and shape of the filament and of the physics of conduction from a solid to a gas, established the foundation for the gas-filled tungsten lamp.  The knowledge gained in these investigations indicated that a thicker filament lost a relatively less percentage of energy by conduction than a thin one for equal amounts of emitted light.  However, a practical filament must have sufficient resistance to be used safely on lighting circuits already established and, therefore, the large diameter and high resistance were obtained by making a helical coil of a fine wire.  In fact, the gas-filled tungsten lamp may be thought of as an ordinary lamp with its long filament made into a short helical coil and the bulb filled with nitrogen or argon gas.

This development was not accidental and from a scientific point of view it is not spectacular.  It did not mark a new discovery in the same sense as the discovery of X-rays.  However, it is an excellent example of the great rewards which come to systematic, thorough study of rather commonplace physical laws in respect to a given condition.  Such achievements are being duplicated in various lines in the laboratories of the industries.  Scientific research is no longer monopolized by educational institutions.  The most elaborate and best-equipped laboratories are to be found in the industries sometimes surrounded by the smoke and noise and vigorous activity which indicate that achievements of the laboratory are on their way to mankind.  The smoke-laden industrial district, pulsating with life, is the proud exhibit of the present civilization.  It is the creation of those who discover, organize, and apply scientific facts.  But how many appreciate the debt that mankind owes not only to the individual who dedicates his life to science but to the far-sighted manufacturer who risks his money in organized quest of new benefits for mankind?  A glimpse into a vast organization of research, which, for example, has been mainly responsible for the progress of the incandescent lamp would alter the attitude of many persons toward science and toward the large industrial companies.

The progress in the development of electric incandescent lamps is shown in the following table, where the dates and values are more or less approximate.  It should be understood that from 1880 to the present time there has been a steady progress, which occasionally has been greatly augmented by sudden steps.