Fluorescent, High Intensity Discharge, Metal Halide, Super Mercury Vapour, High Pressure Sodiums...How on earth do these lights go on, why do they produce such intense heat, and why do they degrade so quickly. Quite different from incandescent, krypton and halogen lights, these bulbs are each uniquely powered on but all share the same common method. With incandescent bulbs current is passed through tungsten metal in a vacuum chamber until the tungsten metal glows. This type of light emission relies on the fact the metal glows (emits light) when subjected to extreme heat provided by the current passing through it. The fact that this bulb relies on extreme heat to force a metal close to its melting point makes it a very ineffecient bulb since most of the electrical energy is utilited in producing heat first to achieve light. The metal glowing filament inside the bulb would instantly oxidize and burn out in normal atmospheric conditions hence it has to be isolated in a vacuum where no oxygen is present. This nifty trick slows down the metal's reaction to oxygen prolonging its life span but will eventually burn out as oxygen will inevetibly leak into the vacuum chamber. Halogen and Krypton bulbs use the same principal as an incandescent bulb but instead of a vacuum chamber, they use a sealed environment injected with halogen or krypton gases. Again, prolonged use of these bulbs will breach the gas sealed chamber allowing oxygen to escape in and oxidize the filament in time. Fluorescent bulbs work in an entirely different way than these bulbs. Fluorescents require no metal glowing filament to emit its light hence it runs a lot cooler. A glass tube is coated with phosphorus and vacuum sealed at both ends with a high impedence cathode at each end. When a high voltage is passed through this tube via the cathodes, the electrons on the phosphorus atoms, gets excited and jumps to the next outer ring or shell absorbing this extra induced energy brought forth by the high voltage. These excited electrons do not stay in an "enlightened" state for too long as that makes the phosphorus atom highly unstable and jumps back to its original state all to willingly. When these electrons return to their normal state they must "dump" the energy that they initially absorbed. These expelled energy packets comes to us in the form of light packets. Now there are many electrons in each atom and many shells...where each electron will jump to and how far each will jump is unknown but given a certain time frame it is possible to hypothesize how many of them will jump to each shell and what shell. With this hypothesis it is possible to determine the light packets dumped hence the light spectrum a tube of phosphorus will produce. The voltage coming out of your wall isn't enough to induce this type of "electron" hopping so a ballast is required. Dismantling a ballast you will generally find a transformer (used to step up the voltage), a capacitor (used to supply additional current during sudden demand situations during initial turn on), and a starter (used to create that super high voltage spark required to commence the whole process) HIDs and Metal Halides use the same type of principal and similar ballasts to produce light but different gasses. The problem with these bulbs is that they produce a lot of heat as a byproduct hence rendering them ineffecient. Nonetheless this method of producing light is still a heck of a lot better than a metal filament. The HPS bulb uses an even higher techinique to produce its light. It deals with a problem that has plagued light bulbs since it was developed, wasted energy in the form of heat. The heat in a HPS bulb is not wasted energy and instead is put to use as part of its method of light production. Sodium gas is injected into a sealed chamber as the other bulbs. The bulb is ignited (via the ballast) just like the other bulbs. As the heat builds up in the sealed chamber due to the high voltage and current, pressure increases dramatically. Sodium gas performs best under high pressure environments so the higher the heat, the higher the pressure, the more light is produced. In a very short period of time the degradation of these light is dramatic. The reason for this is the high temperatures causing high pressured environments in all the bulbs. The gas injected sealed chambers, once pressurized, slowly pushes these gases out. The less gas in the bulb the less light. If you examine these high output bulbs carefully you will notice that there is a long rod or a separate glass chamber inside the huge blub. That is where the gas is stored. The actuall lens of the bulb is more than just a lens. It also serves as a barrier to collect the leaked gases and designed to implode under extreme conditions. The ballasts for each of these bulbs are similar. They all have a step up transformer; but each steps up to different voltages. They each have a capacitor and some contain a starter. Now you know...
