Technical information
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LED is an abbreviation of Light Emitting Diode. LED is a semi-con-
ductor which when electrically stimulated emits light (also called
electroluminescence). The light colour emitted is dependent on
the materials used during manufacture. The basic colours manu-
factured are red, orange, green and blue. White light is produced
by mixing the three dierent colours: red, green and blue (RGB) or,
which is more common, a blue LED equipped with a luminescent
material that converts the emission to yellow light. The sum total is
white light.
White LEDs
White LEDs are available in warm, neutral white as well as cold
colour temperatures (2700–8000 K). Colour reproduction (Ra) can
vary, depending on the choice of LEDs, from 70 to approximately 90.
An LED with a low colour temperature, i.e. a warm light colour, has a
higher Ra value compared with an LED with a high colour tempera-
ture. The luminous ecacy from LEDs is constantly being improved
and rapid development is being made.
The luminous ecacy from white LEDs will soon reach 100 lm/W
i.e. a luminous ecacy corresponding to standard fluorescent
lamps. LEDs with a high colour temperature, i.e. cold light colour,
oer greater eciency than equivalent LEDs with a low colour
temperature. The reason for this is white diodes are basically a blue
diode with a very high colour temperature.
The light distribution from an LED can be controlled/managed via
the use of reflectors, lenses or some form of diusing material. Lenses
are usually directly linked to each manufacturer and the type of LED.
Life and durability
An LED when used correctly has a long life. An LED very rarely fails;
instead the aluminous flux depreciates until it completely disap-
pears. On LED data sheets the life span is stated for when there is
70 % of the luminous flux remaining (L70). This life span is approx.
35,000–50,000 hours for operations within the limit values given by
the manufacturer. A decisive parameter for both life span and lumi-
nous ecacy is that an LED is run at a reasonable temperature.
LEDs neither emit ultraviolet (UV) nor infra-red (IR) radiation. This
makes the light source ideal for use in environments where UV or
irradiation is undesirable, for example, in museums or where food is
being handled. Another advantage of LEDs is that they are not made
up of moving or fragile parts. Manufactured correctly, LED solu-
tions are robust and are resistant to vibration and other mechani-
cal stresses. LEDs do not contain any environmentally hazardous
substances, which simplifies recycling.
LED
Technique
Example of dierent bins, in this case from Philips Lumileds.
Binning
An outcome of LED production is a large variation of both colour
temperatures and luminous flux. The variations are so great that it
is absolutely essential to select a limited assortment. This method
of selection is called binning. Manufacturers divide up the LEDs
after production into dierent groups depending on performance.
The narrower the selection process, i.e. only accepting LEDs from
a single bin, results in a higher product quality. Disadvantages are
that the price can increase while availability decreases. Consequent-
ly, attempts are made to choose LEDs from a number of neighbour-
ing bins.
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