Help With Light Bulbs Terms

Bulb Types


Bulb Base Types

Color Temperature
The color temperature of light refers to the temperature to which one would
have to heat a "black body" source to produce light of similar spectral
characteristics. Color Temperature is expressed in degrees Kelvin (K). Low
color temperature implies warmer (more yellow/red) light while high color temperature
implies a colder (more blue) light. Moreover, the "color temperature" of
a lamp refers to how reddish, greenish or bluish the lamp appears. If the lamp
appears reddish, it has a lower color temperature (e.g., 2500K-3000K) and is
considered to be "warm" in appearance. If the lamp appears to be
bluish, it has a higher color temperature (e.g., 4000K-4500K) and is considered
to be "cool" in appearance.

Warm White: 2500° K to 3000° K
Cool White: 4000° K to 4500° K
Day Light: 6200° K to 6800° K

Color Rendering Index
The Color Rendering Index, or CRI, is a term in photometry used to describe
the effect of a light source on how well it renders colors. In essence, the
Color Rendering Index (CRI) is a numerical system that rates the "color
rendering" ability of fluorescent light in comparison with natural daylight.
If a lamp has a low color rendering index of 50, it does not render colors
very well. If, however, the lamp has a color rendering index of 80 – 95,
its ability to render colors is thought to be very good to excellent. A CRI
of 100 is considered natural daylight and is assigned to the sun itself.

Comments 1

  1. The data on energy efficient lamps is misleading and in some cases completely contradictory.

    E.g. LEDs are currently still less efficient than compace fluorescent. Cold cathode is more efficient than stated.

    I am very surprised that you do not mention linear fluorescent lamps (T5) which are the most efficient source for interior lighting.


    Wolfgang Muller, Arup,
    United Kingdom

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