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Lights and Light Fixtures
Please note:
 For purposes of this discussion, we are using the term light to refer to the type of bulb. The lighting industry uses the term "lamps" and all commercial catalogues and order forms will refer to a specific incandescent lamp or fluorescent lamp. In addition, home improvement stores may refer to lighting fixtures as lights and to light bulbs as bulbs.  
Selecting the right lights and light fixtures is crucial to having an energy efficient lighting system in your business or home. Lights and light fixtures come in a variety of types with a wide range of characteristics. Choosing the appropriate one depends on the lighting task. Cost is another factor to consider. Often, the least expensive to buy is not the least expensive or most energy efficient to operate.
Incandescent Lights
Incandescent lights render color well, are inexpensive, easily dimmed, small, and controllable which is useful for product display. However, incandescent lights have relatively short life spans and are susceptible to failure from heat and vibration. They also have low efficacy (an industry term that refers to the amount of light produced per watt of electricity). Also, most incandescent lights tend to darken with age as tungsten is lost from the filament and deposited on the light walls. Incandescent  lights come in a variety of types and shapes:
  • A Lights - These lights are low cost and commonly used in sizes of A-20 to A-1500 watts.
  • Reflector ( R ) Lights  - These lights are usually more expensive than A lights and offer better control of the direction in which light is cast due to a reflective paint of the light wall. They have a focal point in back of the light, which results in the light being dispersed broadly by the reflective surface. Reflector lights are an appropriate choice for task lighting (because they directly illuminate a work area) and for accent lighting. Reflectors lights are available in R-25, R- 30, R-50, R-75, and R-150 watts. While they have a lower initial efficiency than regular incandescent lights, they direct light more effectively, so that more light is actually delivered than with regular incandescent lights.
  • PAR Lights - Parabolic aluminized reflector (PAR) lights are reflector lights with a lens of heavy, durable glass, which makes them an appropriate choice for outdoor flood and spot lighting. They are available in PAR-75, PAR-150 and PAR-250 watts. They have longer lifetimes with less depreciation than standard incandescent lights.
  • Quartz Halogen Lights - These lights have a short life and low efficacy (the amount of light produced per watt of electricity). They can be a good choice for areas which need lighting on an irregular basis. These lights should not be cleaned.
  • Tungsten Halogen Lights - These lights vary from the standard incandescent by the addition of halogen gases to the bulb. Halogen gases keep the glass bulb from darkening by preventing the filament´s evaporation, thereby increasing lifetime up to four times that of a standard bulb. The lumen-per-watt rating is approximately the same for both types of incandescent lights, but tungsten halogen lights average 94 percent efficiency throughout their extended lifetime, offering significant energy and operating cost savings. However, tungsten halogen lights require special fixtures, and during operation the surface of the bulb reaches very high temperatures, so they are not commonly used at home.
Fluorescent Lights
Fluorescent lights have high efficacy (the amount of light produced per watt of electricity), long life, and low surface luminance. They are cool and come in a variety of colors. Fluorescent lights do require some form of a ballast, an electrical control device that initiates the light arc with high starting voltage. 
Typical fluorescent lights are available in standard high output (HO) and very high output (VHO) configurations. The HO and VHO lights are useful for low-temperature environments and areas where a lot of light is needed with minimal light space.
Fluorescent lights are identified by their T-measure. The T-measure is the measure of the diameter of the light in eighth of an inch. Thus, a T12 fluorescent light is twelve-eighths of an inch (or 1-1/2 inches) in diameter, T10 is ten-eighths of an inch (or 1-1/4 inches) in diameter, and T8 is eight-eighths of an inch (or 1 inch) in diameter.
T12 Lights - Energy efficient T12 lights use about 15 percent less energy than standard fluorescent without a noticeable decrease in light level. For example, a standard 40-watt F40 fluorescent can be replaced by a 34-watt F40 fluorescent.
T10 Lights - T10 lights typically contain phosphors which produce high efficacy and color rendition. They will operate on most ballasts designed for T12 lights.
T8 Lights - T8 lights produce an efficacy of up to 100 lumens per watt, the highest efficacy of any fluorescent light. They will not operate on standard ballasts rated for T12 lights. T8 lights use less of the toxic materials found in larger fluorescent lights, They require a T8 compatible ballast to operate.
Compact Fluorescent Lights (CFLs) - These lights are designed to replace many frequently used incandescent bulbs. They can be used to reduce energy use and power demand by over 70 percent. The lights have a lifetime of at least 10,000 hours and the light produced is similar in appearance to that of an incandescent light. Frequent cycles of short operation hours may however significantly reduce light life. Fluorescent lights with incandescent-type screw-in bases or adapters fit into many incandescent fixtures. Several types are available.
  • The "twin-tube" lights come in 5-, 7-, 9-, 13-, and 26-watt sizes and plug into reusable screw-in ballast/adapters. These ballasts have a rated life of 45,000 to 50,000 hours (about 15 years based on a 5-day, 60-hour work week). Direct-wire ballast adapters are also available. Some units come as a complete lamp/ballast unit.
  • Compact fluorescent lights come as a complete lamp/ballast unit with a translucent cover. When the light burns out, the ballast must also be replaced. However, these lights will last up to 10 times as long as standard incandescent lights and are available in 15-, 18-, to 22-watt sizes.
  • Circline lights are fluorescent tubes formed into a circle and can be screwed in to replace incandescent lights. Some models have ballasts built into the light base. Other come with two circular tubes - one within the other offering a wider selection of wattages. A 32-watt circline light provides the same amount of light as a 100-watt incandescent for one-third the energy cost.
Compact Fluorescent Replacements
Compact Fluorescent Replacements
40-watt A lamp9-watt
60-watt A lamp13 or 15-watt 
75-watt A lamp23-watt
40-watt reflector16-watt with reflector
100-watt A lampTwo 32-watt
High Intensity Discharge (HID) Lights
HID lights are the most efficient lighting sources available today. They create up to one-third less heat and last up to 24 times longer than incandescent lights. Most parking lots, shopping centers and sport arenas now use HID. They can also be considered for indoor use in many applications. Despite their advantages, these lights do have some special considerations. Like fluorescents, they need special ballasts. They have a warm-up time of three to seven minutes, and a restrike time (the delay between off and back on again) of five to ten minutes. The three types of HID lamps are mercury vapor, metal halide, and high-pressure sodium.
Mercury Vapor Lights - These lights are most frequently used outside for parking and security lighting. The lights have a white or blue-white light and limited color rendition. These are the least efficient of the HID lights (slightly less than fluorescents) and should be replaced with more efficient metal halide or high-pressure sodium lights where possible.
Metal Halide Lights - Metal halide lights provide the best rendering of all HID lights. They can be used for merchandise display, entry lighting, or in any situation where color rendition is important, and are frequently used for indoor security and sports lighting.
High-Pressure Sodium Lights - These lights are the most efficient and economical of the commonly used high intensity discharge (HID) lights. Because of their warm golden light and limited color rendering, they are most  suitable for outdoor situations. They are most frequently used as security and outdoor lighting, or in indoor areas, such as warehouses, where color rendering is unimportant.