Characteristics

vorteil005

Incandescent lamps emit heat, whereas light diodes do not. They emit light in a limited spectral segment, the light is almost monochromatic. They are therefore – compared to other light sources, where color filters have to filter the major part of the spectrum – very effective for signal installations.
 

The lifetime of an LED is defined as the period during which the light of the LED has fallen to half of its original intensity. Light diodes are getting weaker and weaker in their light intensity, they usually do not fall out. Light diodes are shock resistant. They do not have a hollow body, which could implode. Their lifetime depends on the respective semiconductor material and the operating conditions (heat, electric current). The indicated lifetime ranges from several 1,000 hours in the case of 5 W LEDs to more than 100,000 hours in the case of LEDs operating with low powers. High temperatures (e.g. through high voltages) shorten the lifetime of LEDs drastically.

 

The short switch periods of LEDs are very important, e.g. in optoelectronics. The modulation frequency can amount up to 100 MHz.
Light diodes have an exponentially increasing current-voltage-curve. During their operation the electric current has to be limited by an additional construction element, in the simplest case a resistor or a constant power source. In this case a more or less intensive and in most of the cases unintended alteration of the nominal current (and therefore also alterations in the light intensity) and even the destruction of the light source can be avoided effectively. The power input varies from model to model between 2 mA (e.g.: miniaturized SMD LED), 20mA (e.g.: 5-mm-LED) and abt. 700 or more mA in the case of LEDs for illumination purposes. The forward voltage ranges in this case from 1.3 V (infrared LED) to abt. 4 V (InGaN-LED: green, blue, UV).

White LED

Different procedures are used to produce white light with light diodes:
Three light diodes in the colors red, green and blue (RGB) are connected with each other and produce white light (used for: displays, effective illumination). This can be obtained either by separate LEDs or by three LED-chips in one housing. White light can also be obtained by connecting only two LEDs in the colors blue and yellow.
The LED-chip is covered with fluorescence coloring. Similar to fluorescent lamps, high-energy short-wave light (blue/UV light) is transformed into low-energy long-wave light. Through the correct selection of components the additive color mix brings White as result. The selection of the colorings varies in this case with the employed materials. Either you excite different colorings (e.g.: RGB) with one UV-LED, whose combination produces white light, or you take a blue LED as base and use only one coloring (yellow, in most of the cases Cer-endowed YAG).
The use of several colorings is more expensive and results in a lower light output, but it allows to obtain good color reproduction characteristics (color reproduction index Ra 90).