We are all familiar with incandescent bulbs, which have been until relatively recently been the most popular sort of bulb.
A voltage is placed across a metal filament held in an inert gas like argon, neon or nitrogen, in order to stop the gas from reacting with the filament and allowing the bulb to live longer. The filament has a high resistance to the current flowing through it, and this heats the filament, causing the atoms in the filament to vibrate. As the atoms vibrate, they then radiate energy in the form of light.
An important point that can be made here, is that all vibrating atoms and molecules will radiate somewhere on the electromagnetic spectrum. The hotter they are, the faster they vibrate, and thus the higher the energy (and frequency) the photons are that they emit.
A problem with this sort of lamp, is that they are very inefficient. Because the light is generated by heating, large amounts of energy is lost in unwanted heat. Also as the filament is heated, it slowly evaporates over time and eventually breaks, leading to a relatively short lifetime. It is mainly for these reasons that there is a move to using energy saving bulbs, which both have a longer life, and also produce the same amount of light for less energy input.
