Common Lighting Types
Light-emitting diodes (LEDs) are the most cutting-edge energy-efficient outdoor lighting option available at this time. These bulbs do not have filaments and instead use semi-conductor technology to light the bulb. LEDs present many advantages over traditional light sources, including lower energy consumption, longer life, improved robustness, smaller size, and faster switching. However, they are relatively expensive and do not work well in extreme heat. They do work well in the cold and extreme cold.
High Intensity Discharge - A high intensity discharge light is also called an HID light. There are several kinds of HID lights, including:
- Metal Halide
- High Pressure Sodium
- Mercury Vapor
Metal halides produce high light output for their size, making them a compact, powerful, and efficient light source. They operate under high pressure and temperature, and require special fixtures to operate safely. These bulbs have a long re-strike time and it can sometimes take a half-hour to an hour after they are turned on for the bulb to gain full brightness.
High Pressure Sodium bulbs contain sodium oxide and operate under high pressure to produce a dark pink glow when they are first turned on, and a pinkish orange light once they have warmed up.
Mercury Vapor bulbs are coated in phosphor and offer better color rendition than high pressure sodium for night applications. The light from a mercury vapor is distinctly blue-tinged. These bulbs have a long life, but over time, their light output drops off to less 50%, but they are still drawing full power.
The picture on the right shows a mix of mercury vapor and high pressure sodium lights. The yellow fixtures on the right are high pressure sodium and the bluish fixtures on the left are mercury vapor.
In an incandescent lamp, an electric current passes through a thin filament and heats it until it produces light. These bulbs produce more heat than light, so they aren’t very energy efficient and have a low efficacy. They also have a short lamp life, which means more frequent replacement and high cost in the long run, from the standpoint of both energy and bulb cost .
A halogen lamp is an incandescent lamp that has a tungsten filament that is sealed into a compact, transparent envelope is filled with an inert gas and a small amount of halogen, such as iodine or bromine. A halogen lamp can operate its filament at a higher temperature than a standard gas-filled lamp of similar power without any loss of operating life. This gives it a higher efficacy, usually ranging from 10-30 lumens per watt. Halogens have a smaller size than HID, so they can work well in doorways and in wall fixtures, also called wall packs. They’re also sometimes used in areas to produce heat, such as the halogen lamp warming the chicks in the photo at right.
A fluorescent lamp is a gas-discharge lamp that uses electricity to excite mercury vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes the phosphor to fluoresce, producing visible light. Unlike incandescent lamps, fluorescent lamps always require a ballast to regulate the flow of power through the lamp. However, a fluorescent lamp converts electrical power into useful light more efficiently than an incandescent lamp. It is called a linear fluorescent if it is a straight tube. Usually these come in 2-foot, 4-foot, and 8-foot options. You might also see them in a U shape, and commonly called a u-tube. A fluorescent that is shaped like a circle is commonly called a circuline fixture. You can look at the label imprinted on the bulb to see what kind of fluorescent tube you have. The example in the photo at right shows an F32T8, which means that the bulb is a 32-watt T8 bulb. This wattage is common for a 4-foot T8 bulb. If it were a T12 bulb, it would be labelled with 40 watts.
A compact fluorescent, also known as a CFL, is a small fluorescent lamp that has a twisted shape, to approximate the size of an incandescent lamp. CFLs use less energy and have a longer life than an incandescent, but cost more. They typically cost less than an LED bulb.
Induction bulbs are also used in outdoor lighting, particularly in cold areas. These bulbs are similar to a fluorescent light, in that mercury inside the bulb is excited, emitting UV radiation that is converted into visible white light by the phosphor coating on the bulb. These bulbs typically use less energy than an HID and have an instant start, so it does not take a long time for the light to reach full brightness. These lamps also have a longer life than HIDs and work well in extreme cold, like LEDs.