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LIGHT ENGINEERING BASICS
LIGHTLight is a component of electromagnetic radiation causing
a perception of brightness in the human eye.The
wavelengths of visible light range between 380 and
780 nm.
(1 nanometer (nm) = 1/1000000000 m). Blue is the
light of the shortest, red of the longest wavelength.
Electromagnetic waves with short wavelengths are
e.g. X-rays; radio waves or infrared radiation have longer
wavelengths than visible radiation.
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LUMINOUS FLUX
The luminous flux . (unit lumen, lm) is the light output
of a source measured in all directions and weighted
with the spectral sensitivity of the human eye.
The specified nominal luminous flux .Lamp of a lamp
is the luminous flux measured at defined conditions of
the lamp (burning position, electrical data). Lamp is
independent of the luminaires. |
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LUMINOUS INTENSITY I
The luminous intensity . (unit candela, cd) is the radiant
power of a lamp emitted in a certain direction or
angle. The luminous intensity is a characteristic feature
for both lamps and luminaires or reflectors.
In the case of a BLV EUROSTAR, the highest luminous
intensity can be found around the centre axis.
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ILLUMINANCE E
The illuminance . (unit lux, lx) is the luminous flux impinging
a certain unit of area. For artificial lighting
there are standards of requested illuminances in different
situations. If for example a lamp emitting 1000
lm impinges a table of 1m2 area with half of its light,
the illuminance on this table is 500 lx. |
LUMINOUS EFFICACY h
The luminous efficacy h (unit lumen/Watt, lm/W) is a
measure for the economic efficiency of a lamp. It measures
the relationship between emitted luminous flux
and consumption of power.
COLOUR TEMPERATURE AND LIGHT COLOUR
The light colour of a lamp can mostly be characterised
by the colour temperature (unit Kelvin, K).
It is defined by a comparison to the so called black body
radiation. The designated colour temperature of a
lamp is the most similar temperature in K which a
black body would have when heated up to this temperature.
The higher the colour temperature, the more
“blueish” or cold the light appears to be.
The clear classification of a colour temperature of a
lamp is not always possible. Therefore for COLORLITE
there is no correlated colour temperature. The light
colour is designated by chromaticity coordinates or dominating
wavelenghts.
Spectrum of a low voltage halogen lamp:
All light colours are present.
Spectrum of a discharge lamp, colour
ww (warm white): The mixture of many
discrete lines gives white light with good
colour rendering.
Spectrum of a COLORLITE green: Mostly
only green light is present.
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SPECTRAL DISTRIBUTION OF A LAMP
The spectrum of a lamp is the amount of the different
wavelengths/colours which a lamp emits.
A halogen incandescent lamp has a so called continuous
spectrum i.e. there are equal units of light of
every wavelength.
The spectrum of a discharge lamp consists of many discrete
lines. The mixture of these lines makes the
light colour of the lamp. |
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Illumination with high-pressure sodium lamp.
Illumination with metal-halide lamp ww (warmwhite).
Illumination with metal-halide lamp ww (warmwhite).
Example: Illumination of an object with a high-pressure sodium lamp and metal halide lamps: the lower the colour rendering
index, the worse the colours of the illuminated object can be observed.
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COLOUR RENDERING The colour rendering properties of a lamp are defined
by the colour rendering index Ra. The colours of our
environment are seen as natural when the illuminating
artificial light sources contain all spectral colours. The
value of best colour rendering is 100 or 1A. It defines
the measure of congruence of the colour of an object
with its occurrence under the lamp defined as standard.
Because of their spectral composition, lamps
can have very different colour rendering properties despite
having the same light colour.
For example, a high pressure sodium lamp and a
warm white metal halide lamp both emit warm white
light, but the sodium lamp has inferior colour rendering. |
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