Lighting Research Center

Advancing the effective use of light for society and the environment

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How do I choose light sources?

Light sources, or lamps, used in residences, fall into three categories: incandescent [common and halogen, which includes Parabolic Aluminized Reflector Lamps (PAR)], fluorescent (linear and compact), and high intensity discharge (HID).

Lamps emit light that is measured in lumens. The lumen output of a lamp depends on the lamp type and its wattage. For the same lamp type, the lower the wattage, the lower the lumens emitted by the lamp. However, fluorescent lighting systems and HID lighting systems provide more light per watt than incandescent lamps. Depending on the application, fluorescent lamps are usually more cost effective than incandescent lamps. Metal halide lamps (one type of HID lamp) give a lot of light for relatively lower wattage, but they take several minutes to achieve full brightness.

a. Common incandescent b. PAR c. Compact Fluorescent
d. Linear Fluorescent e. Metal Halide

  • Fluorescent lamps last 10 to 20 times longer than common incandescent lamps, reducing the number of times one has to get up on a stepladder to change the lamp. Current technology has overcome many problems associated with fluorescent lighting systems. Fluorescent lamps are available with excellent color, plenty of light, no buzz or flicker, and they can be dimmed.
  • The color characteristics of lamps are measured in two ways: correlated color temperature (CCT) and color rendering index (CRI). CCT is a measure of the color of the illumination produced by the lamp; "warm" lamps have a low CCT, and the illumination appears yellowish-white, whereas "cool" lamps have a high CCT and the light appears bluish-white. CRI characterizes how well the illumination produced by the lamp makes objects appear "natural." Remember, both CRI and light level affect color rendering; the higher the illuminance on the task, the more "natural" colors will appear.
  • Incandescent lamps have a low CCT and a high CRI.
  • Fluorescent lamps can have nearly any CCT and can have medium to high CRI.
  • Metal halide lamps usually have high CCT and medium to high CRI.
Some tips for choosing a light source
  • Fluorescent lamps are a good choice for residences, but to have flicker-free, quiet operation, an electronic ballast is required.
  • For good color properties in residences, request fluorescent lamps with a CCT of 2700 to 3500 K and a CRI of at least 80 or above.
  • Compact fluorescent lamps can produce the same amount of light for about 1/3 the wattage of a common incandescent lamp. Just make sure the compact fluorescent lamp fits completely inside the luminaire to avoid seeing the lamp itself. Also, high-quality compact fluorescent lamps always have the ENERGY STAR label on the package.
  • Fluorescent lamps and compact fluorescent lamps are cooler to touch than incandescent lamps. Incandescent lamps can be a burn hazard in task lights.
  • If incandescent and fluorescent (or compact fluorescent) lamps are used in the same room, choose fluorescent lamps with CCT of 2700 to 3000 K to match the warm color of light from incandescent lamps.
  • The light-emitting filament in a common incandescent lamp is very bright when the lamp is operated at maximum power (i.e., without dimming). If it is not possible to shield the incandescent lamp from view, select a bulb with a frosted finish to help reduce glare.
  • To concentrate light onto a specific area (e.g., a countertop or a work of art on the wall), use a halogen PAR incandescent lamp. The table below illustrates how PAR lamps provide higher illuminances than common incandescent and compact fluorescent lamps. Remember, recessed downlights add to the light produced by ambient lighting.
Recessed Downlights (5" Aperture-6 3/4" deep)
(Illuminance in footcandles)
Incandescent Compact Fluorescent Lamp
Common PAR(30) (Quad tube)
75W 100W 50W 75W 13W
5 7 58 65 4

Note: The calculated illuminance levels (center of the beam) are based upon a common A19 incandescent lamp, a PAR 30 lamp, and a compact fluorescent quad-tube lamp. These lamps were assumed to be in a Lightolier Lytecaster #1005 with Step Baffle mounted 66 inches (in.) above the countertop [8 feet (ft) ceiling height].

Illuminance is defined as the amount of light falling on the task.

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