However, to start current flowing through a gas at high pressure requires a very high voltage. Once the current begins to flow, the voltage is reduced. The ions and electrons produced are accelerated in the electric field, contributing to the current and colliding with and exciting other molecules. For this reason, these lamps are much brighter and more suitable for outdoor lighting. Gas-discharge lamps are more efficient than incandescent lamps.
Incandescent lamps operate by heating a tungsten filament so hot that it glows.
A great deal of the energy consumed in this process is used to heat the filament. At each end of the tube is a mirror. Some of the light emitted by the excited gas molecules becomes trapped between the mirrors, being reflected back and forth repeatedly. When this light passes excited gas molecules, it stimulates them to emit their energy parallel to the passing light. The effect of this is to amplify the intensity of the light beam trapped between the mirrors.