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The following are a few of the
characteristics that must be
understood when looking at your
present lighting system: |
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Color Temperature |
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A light bulb looks like a certain
color because of the Color
Temperature. It is not actually how
hot the light is but how the
radiator reaches a certain
temperature to produce the color of
the bulb. The radiator is a
laboratory term for a blackbody. The
blackbody will change different
colors as the temperature increases
from red to orange to yellow, white,
blue-white and finally blue. This is
why at night time when you look out
at all of the lights from a distance
some will appear to be different
colors, some more yellow than
others. This is because the lamp's
color temperature causes the color
variation. |
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Light Output |
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There are
several ways to measure light
output: |
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Candlepower (cp): |
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Luminous
intensity expressed in candelas. |
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Lumens |
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SI unit of
luminous flux. Radiometrically, it
is determined from the radiant
powder as in luminous flux.
Photometrically, it is the luminous
flux emitted within a unit solid
angle (1 sr ) by a point source
having a uniform luminous intensity
of 1 cd. |
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Illuminance |
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The areal
density of the luminous flux
incident at a point on a surface. |
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Brightness
(of a perceived aperture color) |
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The attribute
by which an area of color of finite
size is perceived to emit, transmit,
or reflect a greater or lesser
amount of light. No judgment is made
as to whether the light comes from a
reflecting, transmitting or
self-luminous object. |
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Luminaire
Efficiency |
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The ratio of
luminous flux (lumens) emitted by a
luminaire to that emitted by the
lamp or lamps used therein |
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Quality of Light |
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Luminous
Efficacy of Radiant Flux |
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The quotient
of the total luminous flux by the
total radiant flux. It is expressed
in lumens per watt. |
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Color
Rendering Index (CRI) |
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This is how
you perceive the color of an object
under a light fixture. Not all bulbs
will produce the same type of light.
Below is an index of CRI and will
indicate which bulb will have the
least amount of color shift. It is
rated on a scale of 0-100 with 100
being the best: |
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75 - 100 |
Excellent |
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65 - 75 |
Good |
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55 - 65 |
Fair |
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0 - 55 |
Poor |
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Definitions from
The IESNA Lighting
Handbook-Reference & Application
- written by the Illuminating
Engineering Society of North
America. Editor-in-Chief - Mark S.
Rea, Ph.D., FIES. |
