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LED technology
Technical data
The principles of LED technology
The basis for light generation inside a Light Emitting Diode (LED),
a solid-state semiconductor, is the conversion of electrical energy
directly into light.
On its most basic level this can be seen as an electron that moves
from one material into another while losing an amount of energy. Due
to the law of conservation of energy, this loss of energy needs to be
converted and, inside a LED, this energy is converted into radiation
energy composed of light in the visible part of the spectrum, and a bit
of infrared radiation dissipated as heat.
The LED is comprised of two semiconductor regions, a positive
electrically charged or p-region and a negative electrically charged
or n-region, see diagram 1. In the p-region there is a shortage of
electrons and in the n-region a surplus of electrons. When voltage
isappliedacrossthesetworegions,currentbeginstoowand
electrons move across the p-n junction, from the n-region into the
p-region. The process of an electron moving through the p-n junction
releases energy. The dispersion of this energy produces photons with
visible wavelengths. The higher the energy released, the shorter the
wavelength becomes. Low energy photons will emit in the infrared
part of the spectrum, and as the energy increases, the color of the
light will change from deep red, via yellow, green, cyan and blue to the
ultra-violet part of the spectrum – in fact it follows the colors of the
rainbow.
Diagram 1. LED composition with the electrically charged p- and n-regions and
the p-n junction emitting light.
White light and RGB (red, green and blue)
A white LED consists of a blue LED chip and a yellow phosphor
coating, see diagram 2. The blue photons generated in the
semiconductor chip can either pass the phosphor layer unaffected, or
be converted into yellow photons. These two colors – blue and yellow
– combine to produce white light.
Diagram 2. White LED, the principle of white light generation.
It is also possible to generate white light with the aid of a red, green
and blue LED. Such LED array systems are called RGB systems.
Normally the RGB systems are used to make different color effects.
With a RGB system all colors of light within the color triangle can be
produced.
Graph. Color triangle for a RGB system; all colors within the triangle can be
reproduced.
Characteristics and benets
Onthenextpageyouwillndanoverviewofthecharacteristics
andbenetsofLEDs.Inthevariousindoorandoutdoorapplications
different advantages will be important. Architectural applications will
usethevividcolorsanddynamiccolorcontrol,whereasthetrafc
signal market is focused on maximizing energy savings and reducing
maintenance costs to practically zero.
Indoor_2008_Chapter_12_LIS.indb 8 20-05-2008 14:32:56