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The Light Emitting Diode story
1907: Henry Joseph Round discovers
the physical effect of electroluminescence.
But as he is working on a new radio
direction finding method for marine
vessels this discovery is initially
forgotten.
1962: The first red luminescence
diode, type GaAsP, is launched. 1971:
LED in other colors are available: green,
orange, yellow. There are continual
improvements in the output and effectiveness
of all LEDs.
1993: Highly efficient InGaN
diodes emitting in the blue and green
spectrum are demonstrated. The conditions
for creating white light are met.
1995: The first LED with white
light created by luminescence conversion
is launched.
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For more than 30 years, LED have been used in
various industrial applications from switch
cabinets to measuring instruments, in consumer
products such as HiFi- equipment, telephones
or personal computers, in traffic signal installations
for road and railway or in indoor and outdoor
automotive lighting. automotive lighting.
In the last few years the efficacy of colored
LED increased up to amazing 100 lm/W and more
depending on the color and driving conditions.
A trend which will proceed in the future.
As today's white LED reach efficacies up to
40-100 lm/W (efficiency depends on color temperature
and color rendering) - they are more and more
used in general lighting. In emergency lighting
as well as decorative lighting, they are already
established in implementation area. Today, also
applications such as illuminated advertising
benefit from the advantages of LED, particularly
by using colored LED-modules.
Basic principles
of LED (Light Emitting Diodes)
- LED consists of several layers of semiconducting
material
- When an LED is operated with DC voltage
light is generated in the active layer
- The generated light is radiated directly
or by reflections -In contrast to lamps,
which emit a continuous spectrum, an LED
emits light in a certain color
- The color of the light depends on the
used material
- Two systems of material (AllnGaP and
InGaN) are used in order to produce LED
with a high luminance in all colors from
blue to red and also in white (luminescence
conversion). Therefore different voltages
are necessary in order to operate the diode
in conducting direction.
The production
of white light
To produce white light, the light of blue LEDs
is passed through yellow phosphors. The composition
of the phosphor determines the light color.
The Chip Level Coating (CLC) process developed
and patented by OSRAM ensures a degree of homogenity
in the light produced that other processes cannot
achieve. By selecting appropriate white LEDs,
it is possible to offer LED systems with the
same light colors as fluorescent lamps (Warm
White, Neutral White and Daylight).
Innovative LEDs
offer a number of technological advantages
- Low energy consumption
- Extremely long life
- Very low early failure rate
- Smallest dimensions
- Shock and vibration resistant
- No ultra-violet or infrared radiation
- Low wattage
- Almost no heat generation
- Directed light - Lambertian emitter
with beam angle 120°
- High color saturation
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