A fluorescent lamp is a “gaseous discharge” light source. This energy causes the phosphor coating on the inside of the tube to “fluoresce,” converting the ultraviolet into visible light. Fluorescent lamps have two electrical requirements. To start the lamp, a high voltage surge is needed to establish an arc in the mercury vapor. Once the lamp is started, the gas offers a decreasing amount of resistance, which means the current must be regulated to match this drop. This is why fluorescent lamps — and other discharge light sources — must be operated by a ballast.
Halogen bulbs work very similar to Incandescent technology but improve the process. Halogen lamps deliver a crisp, white light and render colors even better then incandescent technology. Gas is inserted at a high- pressure and sealed off. The halogen bulb operates at higher temperature, which causes the tungsten in the filament to evaporate.
Incandescent lighting technology has been around since Thomas Edison. As the oldest of the lighting technologies, it’s also the least efficient. Incandescent lamps product less lumens per watt than any other technology, due mostly to the heat they produce. Higher wattage incandescent lamps can no longer be produced in the US, with lower wattages on the chopping block in the years to come.
LEDs differ radically from traditional light sources in that there are no glass bulbs or filaments to break, or electrodes to decay. Instead, LEDs are solid state light sources – basically, a chemical chip embedded in a plastic capsule. When the chip is energized by applying a voltage, it emits visible light, the color depends on the chip’s chemical composition. The light can then be focused, routed or scattered using lenses, waveguides or diffusers. Because LEDs run on direct current, they must be operated with a transformer-type power supply.
The technology in high-intensity discharge (HID) bulbs is in some ways similar to fluorescent technology: an arc is established between two electrodes in a gas-filled tube which causes a metallic vapor to produce radiant energy.
In addition, the electrodes are only a few inches apart (at opposite ends of a sealed “arc tube”) and the gases in the tube are highly pressurized. This allows the arc to generate extremely high temperatures, causing metallic elements within the gas atmosphere to vaporize and release large amounts of visible radiant energy. There are three main types of HID lamps: mercury vapor, metal halide and sodium.
The names refer to the elements that are added to the gases in the arc stream which cause each type to have somewhat different color characteristics and overall lamp efficiency. Like any gaseous discharge light source, HID lamps have special electrical requirements that must be supplied by a ballast.
With HID sources, however, the ballast must be specifically designed for the lamp type and wattage being used. In addition, HID lamps require a warm-up period to achieve full light output. Even a momentary loss of power can cause the system to restrike and have to warm up again — a process that can take several minutes.
For more information about selecting and identifying HID bulbs, see our article Differences and Identification of HID bulbs