While most folks use the generic term “bulb,” the correct term for glass-enclosed balls and tubes is lamp. Lamps come in a variety of shapes and sizes. Incandescent lamps are glass enclosures from which the air has been evacuated and replaced by an inert gas. This protects the filament from overheating, extending its longevity. These lamps require no external control and are connected directly to the home electrical system through fixture sockets. Incandescent lamps are not energy efficient since about 90% of the energy consumed is turned into heat instead of light.
Fluorescent lamps are glass tubes filled with a combination of a low-mercury gas and either argon, neon, krypton or xenon. The interior of the tube is coated with a phosphorescent or fluorescent coating. When the filaments are energized, the mercury vapor is excited, which will cause the coating to glow. Fluorescent lamps cannot be connected directly to the home electrical system, but must have the voltage regulated by a ballast unit. Compact fluorescent lamps, called CFLs, are small versions of the larger tubes; however, they are manufactured with built-in ballasts and can be screwed directly into most lamp sockets. Fluorescent lamps and CFLs are much more efficient than incandescent lamps and have a longer life cycle.
Halogen lamps use a variation of the incandescent lamp technology. These lamps use a tungsten filament that is encased in a glass container, filled with halogen. Their candlepower output is higher than an incandescent lamp, making them more efficient. Halogen lamps are often used in flood light applications. A smaller version is sometimes used in decorative accent lighting.
The most energy efficient lamps available to homeowners are light-emitting diode lamps, also known as LEDs. However, they are also the most expensive. The life cycle of an LED lamp can be as high as 100,000 hours of continuous operation. LEDs are commonly used in night lights and decorative lighting.