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Lighting measurement terminology |
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 Luminous
Flux : |
Luminous flux describes the light power
emitted by a light source per unit interval. |
Unit : Lm |
| Luminus
Intensity : |
The luminous intensity is the luminous flux emitted
from a point per unit solid angle into a particular direction.
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Unit : Cd |
| Lux
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Lux means the measure of light emitted into a certain
unit area. It also represents the brightness value of
certain spot. Lux = Total Lumens ÷ Area in Square Meters.
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Unit : Lux |
| Luminance
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Luminance means the radiance degree of the objects
or lighting source. It is used to describe the brightness
of orthogonal projection in unit area. |
Unit : Nit, Cd/m2 |
| Chromaticity
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Chromaticity is a measuring value which is used to describe
the induced intensity of human eyes toward color vision. |
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Color
Rendering Index |
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Color Rendering Index (CRI) is numerical
system that rates the "color rendering" ability
of a source light in comparison with natural daylight. |
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An illuminant with high CRI shows vivid performance
with color and the appearance of the object in eyes will
be more natural. |
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The measurement criterion is based on natural daylight,
which has a CRI of 100. |
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Artificial light source – In choosing the right color
for a specific application, the value CRI 90 means the
light source is 90% close to natural daylight . |
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Color
Temperature
Color temperature is a simplified way to characterize
the spectral properties of a light source. Technically, color
temperature refers to the temperature to which one would have
to heat a theoretical "black body" source, like iron,
to produce light of the same visual color. During the heating,
the theoretical "black body" source changes its color
in the following order: red, orange, yellow, onix, white, sky-blue.
When it is heated to red, the temperature is about 527° C or
800 K. (Standard unit for color temperature is Kelvin (k). The
Kelvin unit is the basis of all temperature measurement, starting
with 0 k (= -273.16° C) at the absolute zero temperature.) Low
color temperature implies warmer (more yellow/red) light while
high color temperature implies a colder (more blue) light. |
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List of Color Temperatures and Different
Light Sources |
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Color Temperature
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Light Source |
| 20000~25000K |
Sunny blue sky light |
| 6000K |
Sunny daylight from plateau |
| 5300K |
Sun light with cloud sheets |
| 5000~4000K |
Cold Fluorescent lamp |
| 4600~4000K |
Metal halide lamp |
| 4100K |
Full moon |
| 3750~3450k |
Mercury lamp |
| 3000K |
Halogen lamp |
| 3000K~2500K |
Warm fluorescent lmap |
| 2700K |
Filament lamp |
| 2250~1950K |
High pressure sodium lamp |
| 2000K |
Candle |
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Lighting Efficiency（lm/W） |
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The
lm generated by each Watt. The more the luminance generated
by each watt. |
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The
higher lighting efficiency is more power saving. |
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Lighting
efficiency varies according to power, lamp types, and
operating conditions. |
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