Light Sources

The performance of any light fixture depends very much on the light source (bulb) used. Different sources produce different lighting effects, and many sources have widely varying performance.

Lighting Measurement Terminology


The amount of electricity consumed by a light source.


The amount of light that a light source produces.


Lumens per watt.


The amount of light reaching a subject.

Today’s energy-efficient light bulbs, such as compact fluorescent or LED, produce significantly higher amounts of light for every watt of energy used. It is most important to remember, however, that wattage does not measure light output; it only measures the electrical consumption of the bulb.


General service bulbs are inexpensive and readily available in a wide variety of wattages and shapes. They produce a yellow-white light that is emitted in all directions, and are used in almost all types of fixtures, including table and floor lamps, ceiling fixtures, wall fixtures and chandeliers. They are available in either a clear or frosted finish.

Types of bulbs:

  • General (A)
  • Globe (G)
  • Decorative (candle and flame shapes, teardrop and other shapes) (D)

Federal legislation implemented in 2012 has increased the energy-efficiency of standard incandescent bulbs. Check with your Kay lighting showroom for more information on these changes and the new types of bulbs now available.

Reflectorized bulbs have a reflective coating inside the bulb that directs the light in one direction, providing better beam control than general service lamps. All reflectorized bulbs are available in a variety of beam shapes such as flood (FL), narrow flood (NFL), spot (SP) and narrow spot (NSP).

Bulged reflector (BR) bulbs provide a soft quality of directional light, and they are very common for recessed and track lighting.


Tungsten-halogen sources produce a quality of light that is brighter and whiter than standard incandescent bulbs. They also have a longer life and provide more light per watt than standard incandescent bulbs. Tungsten-halogen bulbs are available in both standard voltage (120 volts) and low voltage (12 and 24 volts). Low-voltage bulbs require a transformer to step down the voltage from 120 volts to 12 volts or 24 volts.

Line Voltage (120 volt)

PAR 16, PAR20, PAR30 and PAR38 shapes provide better beam control than incandescent R or BR bulbs. They are available in a variety of beam shapes such as flood (FL), narrow flood (NFL), spot (SP), and narrow spot. They are commonly used in track, recessed and outdoor floodlights where a high quality of white light is desired.

A-19 General service halogen bulbs are excellent replacements for standard incandescent, general service bulbs. They are available in the same shapes and sizes and are more energy-efficient than standard incandescent bulbs.

T-3 Double-ended halogen bulbs are used in wall sconces, torchieres and outdoor flood lights. These are not directional bulbs, so the light direction and beam spread is controlled by the fixture.

T-4 Single-ended halogen bulbs come in both mini-can and bayonet base types, and are used in wall sconces, bath brackets, torchieres and pendants. As with the T-3 bulbs, the direction of the light is controlled by the fixture.

Low Voltage (12 volt)

The MR8, MR11 and MR16 (mini-reflectors) provide excellent beam control. They are available in numerous spot and flood beam options. Their miniature size permits their use in smaller track and recessed fixtures. They also are used in outdoor landscape accent lighting fixtures.

PAR36 bulbs provide superior beam control, especially over longer distances. They also are available in many beam spread options, and are used in track, recessed and outdoor landscape accent lighting fixtures.

The T-4 Bi-pin bulb is a miniature bulb used in pendants, halogen desk lamps, and linear, low-voltage track systems. They are used widely in cove lighting conditions and in undercabinet, low-voltage lighting systems.

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

Light Emitting Diode

Light emitting diode (LED) bulbs are available in a wide variety of configurations and can be used to replace standard incandescent, low-voltage, tungsten, halogen, xenon, general service and reflectorized bulbs. In the future, LED bulbs may become the predominant type of light source used in homes.

The light emitting diode (LED) is one of today’s most energy-efficient and rapidly developing technologies. This type of light bulb is more than five times more energy-efficient and can last up to 25 times longer than traditional incandescent bulbs. While LEDs are more expensive, they still save money because they last a long time and use a low amount of energy.


Fluorescent bulbs produce as much as five times the amount of light per watt of energy used than incandescent or tungsten-halogen sources. They are approximately five times more energy-efficient. They also have a rated life from 10 times to 20 times that of incandescent sources.

Compact fluorescent lamps (CFLs) are small fluorescent bulbs that are being used increasingly in all types of lighting fixtures, including chandeliers, wall sconces, surface mounted fixtures, recessed lighting and track lighting. CFL bulbs with a screw-in type of base can be used to replace incandescent lamps in standard lamp sockets.

T8 bulbs with electronic ballasts are commonly used in larger ceiling fixtures. These bulbs are extremely efficient, and because of the electronic ballast, the fixtures turn on instantly and do not hum. These bulbs have been common in commercial projects, and are now being used widely in residential installations. They are available in a wide range of color tones, from warm to neutral to cool.

High-Intensity Discharge

High-intensity discharge (HID) bulbs have a longer life and provide more light (lumens) per watt than any other light source. There are four different types of HID bulbs: mercury, metal halide, high pressure sodium and low-pressure sodium. HID bulbs are mostly used in commercial and non-residential applications. They are sometimes used in residential applications for outdoor security and area lighting.

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