Types of Incandescent Lamps
- Standard incandescent bulbs are common, but inefficient.light bulb image by David Ng from Fotolia.com
In 1879, Thomas Edison conducted his first successful test on his incandescent light bulb. It was a glass bulb under vacuum with a carbon filament inside. As of 2010, the filaments are made of tungsten, and the vacuum has been replaced with inert gas. The inefficiency of the incandescent bulb has been scrutinized, and the U.S. Congress voted in December 2007 to ban their use, beginning in 2012. - According to the U.S. Department of Energy, the standard type "A" screw-in incandescent bulb is the most common light source in use, as of 2010, but is also the most inefficient. The light from these lamps is produced by the application of electric current through a tungsten coil within a glass bulb filled with an inert gas, either argon or nitrogen. The tungsten glows when it is heated and this glow provides light.
A measure of a light source's energy efficiency is its efficacy, or the ratio of light produced versus the energy consumed in units of lumens per watt. Standard bulbs with higher wattage have higher efficacy, but they are still inefficient. The U.S. Department of Energy gives standard type "A" bulbs an efficacy rating of 10 to 17 lumens/watt. - Tungsten halogen lamps are filled with the same inert gas as the standard bulb, but a trace of halogen vapor is added for improved color rendition. In addition, the inner surface of the bulb is treated with a coating that reflects heat back to the filament, effectively recycling the heat to the filament instead of passing it to the outside of the bulb. The gas inside the bulb is under higher pressure than a standard bulb, 100 to 118 psi, and has a higher operating temperature, 480 to 1100 deg F (250 to 600 deg C). The higher pressures and temperatures require a stronger bulb, which are made from high silica glass, fused quartz or aluminosilicate.
Tungsten halogen lamps are more efficient than standard incandescent lamps, but are more expensive. Their higher efficiency, however, makes them cheaper to operate in the long term. The U.S. Department of Energy gives them an efficacy rating of 12 to 22 lumens/watt. - Theatrical spotlights are examples of reflector incandescent lamps.projecteur 5 image by Nathalie P from Fotolia.com
Reflector lamps direct lighting toward a specific area through the use of a built-in lens and reflector. They are used for floodlighting, such as at sports stadiums; spotlighting, like car headlights; and downlighting, such as street lights. There are two types of reflector incandescent lamps, each named for the shape of its reflector: parabolic aluminized (PAR) and ellipsoidal (ER). The U.S. Department of Energy gives reflector lamps an efficacy rating of 12 to 19 lumens/watt.
