Technology of electric lighting has evolved a long way since 120
years ago first incandescent bulbs were invented. Lights are produced by
excited electrons of atoms of certain materials returning to their base states
and releasing enery in forms of photons. Evolution of electric lighting has
been on the materials and the way to excite the electrons.
Incandescent light comes from burning of metals (which usually have high
melting points), nowadays incandescent light bulbs use Tungsten filaments. The
Tungsten filaments can burn up to 5000F. To avoid catching flame, the Oxygen is
vacumed out of the bulbs. The Tungsten atoms, however, evaporate and eventually
the filament will break. To slow down the evaporation of Tungsten, inert gases
are injected into the bulbs (which increses the pressure inside bulbs and
suppresses evaporation). Incandescent lights, however, are not very efficient
because they also produce a lot of heat which is a waste of energy when the
purpose is the light.
Fluorescent lights use electricity to excite mercury atoms which release
ultraviolet photons. The ultraviolet photons in turn excite phosphor atoms to
emit visible white light (phosphor powder coating). Since fluorescent tubes
make use of the invisible light, they are more efficient than incandescent
bulbs.
Halogen lamps
Normal household light bulbs are filled with argon and/or nitrogen. The bulbs
usually end up with their tungsten filaments breaking due to evaporation.
Halogen lamps use a 'quartz envelope' to encase the tungsten filament. (Use of
quartz prevents the glass from melting.) Halogen is added in the quartz
envelope. Halogen atoms can combine with evaporated tungsten atoms and
redeposit them on the filament. This increses the longevity of the filament.
The filament can thus run hotter and produce more light than incandescent
bulbs.