Light+Bulb+Comparisons

What kinds of light bulbs are there?
There are four different light bulb types available for residential use:


 * incandescent
 * halogen
 * compact fluorescent (CFL)
 * LED (light-emitting diode)

Each bulb has a unique technology that gives it its properties such as brightness, lifetimes, efficiencies, etc. Here is a look at each.

Incandescents
The first (successful) light bulb, invented by Thomas Edison, was an incandescent. Its components are shown below:



The filament in an incandescent bulb is made of a very fine **tungsten** metal coil:



When electricity is run through the filament, it heats it up, and it glows brightly.

The filament is protected from simply burning up in oxygen because the bulb is filled with an inert gas, such as nitrogen.

Most incandescents contain a "frosting", which is a coating inside the bulb to soften and filter the light.



Halogen Bulbs
A halogen light bulb is similar to an incandescent, but with a few distinct differences.



One major difference is the use of a halogen element (commonly **bromine**) to prevent decomposition of the filament, and the use of a coating to absorb UV radiation.

Halogens typically last longer than incandescents because of the use of bromine, but they typically use the same wattage.

Compact Fluorescents
A compact fluorescent bulb, or CFL, has no filament like an incandescent or halogen. It operates on a principle similar to a neon sign, where a high voltage is passed through a gas, causing it to glow.

In the case of CFLs, the gas is **mercury**, which vaporizes readily under power.

A CFL has what is called a "ballast", where all the electronics are:



This ballast regulates the electric current and voltage in the bulb.

Why mercury? Mercury's electrons are excited and release UV light when a current is applied. This then reacts with the white frosting inside the tube (a phosphor coating) to produce visible light. This type of bulb would not work without mercury.

While it is toxic, and precautions must be used if a CFL breaks, studies have shown that using CFLs can actually reduce the amount of mercury in the air (and thus water, soil, and foods like tuna) by reducing coal power plant emissions.



Light-Emitting Diodes (LEDs)
 An LED bulb is again quite different than any other bulb. It uses a diode, which is an electronic component that is made from semiconductors like **germanium**.  

 The way this works is that electrons can be absorbed by "holes" in the semiconductor; when they are, they emit photons of light. This happens at low voltages, and is why LEDs last so long and use very little power. == Energy Use ==

A standard incandescent or halogen bulb that uses a tungsten filament is very energy-inefficient. You are probably aware of the amount of heat these bulbs produce. Well, we can't see heat, so as far as a light bulb goes, heat is wasted energy.