Types of Light Sources and Light Bulbs

The performance of any light fixture depends very much on the light source (bulb) used. Different bulbs produce different lighting effects, and many bulbs have widely varying performance. To save energy, select the most efficient light bulb that will provide the type of lighting you need.

Beginning in mid-2011, the packaging on your favorite light bulbs will change. Click here to learn more about the new focus on lumens rather than watts.

Another source is LUMEN, which stands for Lighting Understanding for a More Efficient Nation.  LUMEN is a coalition of 40-plus organizations, with a Steering Committee led by the American Lighting Association, the Alliance to Save Energy, and the National Electrical Manufacturers Association.  The website, www.lumennow.org, provides helpful tips in selecting the correct light bulb for your home.

Lighting Measurement Terminology

Wattage: The amount of electricity consumed by a light source
Lumens: The amount of light that a light source produces
Efficacy: Lumens per watt
Footcandles: The amount of light reaching a subject

Types of Bulbs

Click here to read our FAQs on choosing a light bulb for your home.


Light Emitting Diodes (LEDs) produce light when voltage is applied to negatively charged semiconductors, causing electrons to combine and create a unit of light (photon). In simpler terms, an LED is a chemical chip embedded in a plastic capsule. Because they are small, several LEDs are sometimes combined to produce a single light bulb.

LED lighting in general is more efficient and longer lasting than any other type of light source, and it is being developed for more and more applications within the home. LEDs are currently popular in under-cabinet strips and some types of downlights.

To ensure that you are purchasing an LED bulb with good color quality and energy efficiency that is as good or better than fluorescent bulbs, look for the ENERGY STAR symbol.


Incandescent bulbs produce light when an electric current passes through a filament and causes it to glow. Because they are less energy efficient than other light sources, they are best used for task lighting that demands high levels of brightness.

Beginning in 2012, the U.S. Energy and Independence Act of 2007 will require most incandescent bulbs to produce the same amount of light using less wattage.
Click here to learn more.

The types of incandescent bulbs available include:

Incandescent BulbsGeneral service incandescent bulbs are the inexpensive, readily available light bulbs that most of us think about when we hear "light bulb." They produce a warm, yellow-white light that is emitted in all directions and are available in either a clear or frosted finish. There are three basic shapes:

General (A)
Globe (G)
Decorative (Flame, teardrop and other shapes)

Reflectorized BulbsReflectorized incandescent bulbs have a reflective coating inside the bulb that directs the light in one direction rather than all around.

Reflector (R) bulbs put approximately double the amount of light (footcandles) on the subject as General Service (A) of same wattage.

Parabolic Reflector (PAR) bulbs control light more precisely. They produce about four times the light of General Service (A) and are used in recessed and track lighting. Weatherproof casing makes them suitable for outdoor spot and flood fixtures.

Tungsten-halogen incandescent bulbs produce a brighter and whiter light than other incandescent bulbs. They also have a longer life and provide more light per watt than standard incandescent bulbs, making them a more efficient choice. Halogen bulbs are available in two types: line voltage (120 watt) and low voltage (12 volt).

Line Voltage BulbsLine Voltage (120 volt)

PAR 16, 20, 30 and 38 reflectorized bu  lbs provide better beam control than regular incandescent PAR bulbs. They are available in numerous spot and flood beam spreads and are used in track, recessed and outdoor spot and floodlights.

T-3 Double-Ended bulbs are available in a variety of base types and are used in wall sconces, torchieres and outdoor flood lights. The direction of the light is controlled by the fixture.

T-4 Single-Ended bulbs come in both "mini-can" and "bayonet" base types and are used in wall sconces, bath brackets, torchieres and pendants. The direction of the light is controlled by the fixture.

Low VoltageLow Voltage (12 Volt)

MR8, MR11 and MR16 (mini-reflectors) provide excellent beam control, and their miniature size allows them to be used in smaller track and recessed fixtures. They are also used in outdoor landscape accent lighting fixtures.

PAR36 bulbs provide superior beam control, especially over long distances. They are used in track, recessed and outdoor landscape accent fixtures.

T-4 Bi-Pin bulbs are miniature bulbs used in pendants, halogen desk lamps and linear, low-voltage track systems. They are widely used in cove lighting and undercabinet lighting.

Xenon rigid-loop, festoon and wedge base bulbs have a white light similar to that of halogen but have a much longer life rating (some up to 20,000 hours, much like fluorescent) and operate at lower temperatures than halogen. These miniature bulbs are popular for strip, under-cabinet and cove lighting applications.


Fluorescent bulbs produce light when an electric arc passes between cathodes to excite mercury and other gases producing radiant energy, which is then converted to visible light by a phosphor coating.

They use 1/5 to 1/3 as much electricity as incandescents with comparable lumen ratings and last up to 20 times longer. Compact types are used in smaller, trimmer fixtures such as recessed downlights, wall sconces, close-to-ceiling fixtures, and track lights. Screw-in types can be used in place of incandescents in standard lamp sockets. Available in a wide spectrum of colors. Warm white tones best duplicate the color of incandescents.
Today's fluorescent bulbs come in a wide selection of sizes and can produce warm tones of light similar to those of incandescents.

If your fixtures are on a dimming system, look for fluorescent bulbs labeled "dimmable."

Because fluorescent bulbs contain mercury, it is important to dispose of them properly.

Fluorescent BulbsCompact Fluorescent Lamps (CFLs) are small fluorescent bulbs that can be used in most types of lighting fixtures. The screw-in types can be used to replace incandescent lamps in standard lamp sockets.

T8 bulbs with electronic ballasts are commonly used in larger ceiling fixtures. Because of the electronic ballasts, they turn on instantly and do not hum. They are commonly used in commercial projects and are now being widely used in residential applications.


High-Intensity Discharge (HID) bulbs produce light when an arc passes between cathodes in a pressurized tube, causing metallic additives to vaporize. They have long lives and are extremely energy efficient, but - with the exception of metal halides - they do not produce pleasing light colors. In residential settings, HIDs are most often used for outdoor security and area lighting.

There are four types of HIDs:
Metal Halide
High-Pressure Sodium
Low-Pressure Sodium
Mercury Vapor