Small, robust and energy-efficient, LEDs have evolved in a very short time from signal indicators to stars of the lighting scene. We encounter them in daily life at every turn - in flashlights and garden lights, in office luminaires, illuminating stairs and living rooms.

The powerful mites' many advantages include:

• low power consumption
• low wattage
• extremely long life
• no UV or IR radiation
• virtually no heat gain
• high shock resistance
• extremely low incidence of early failure
• very compact design
• high colour brilliance.
  
  

LEDs burn for up to 50,000 hours. That is nearly six years of maintained operation and makes them a reliable light source for applications where installation conditions are difficult.

Light emitting diode: an electronic semiconductor crystal

LEDs are electronic semiconductor crystals. When an electric current flows through them, they emit red, green, yellow or blue light, depending on the nature of the semiconductor elements.

Initially, the fact that LEDs produce only coloured light severely restricted their scope for application. For a long time, they were used only as signal lights in switches or displays. In the late 1990s, engineers extended the LED colour spectrum, using an internal luminescent coating to enable blue LEDs to produce white light – effectively and economically.

LEDs bring colour into our world

Alternatively, it is also possible to obtain white light by bundling together three different LEDs – red, blue and green. This is the right method wherever changing colours are required. Modern LEDs can mix more than 16 million colours using these three components of the RGB model. From delicate lilac through orange to midnight blue – using pale or bold colours in sequence or in simultaneous pools of separate or intermingling light, LED systems create fascinating atmospheres with soothing or stimulating effects for a special experience.

Dynamic colour sequencing creates particularly attractive effects. Programmed via control modules, colour changes can be rapid or barely perceptible, with intervals ranging from seconds to several hours. Coloured dynamic lighting adds a dramatic dimension to the atmosphere of salesrooms, foyers, even private rooms. It is also popular in wellness centres as an aid to relaxation.

LED luminous efficacy and life

Most of the LED light sources in use are LED modules comprised of several individual LEDs. Whereas the only light colour available in the past was a cold white (light colour > 4,500 K), there are models on the market today that produce a warm white (> 2,800 K) or neutral white light (3,300 to 3,800 K). Light within these colour temperature ranges achieves a colour rendering index between R_a ≥ 70 and R_a ≥ 90. The Ra index for cold white LEDs is between 70 and 80. The luminous efficacy of coloured LEDs reaches more than 50 lm/W, that of white LEDs is currently 30 lm/W.

The life of today's generation of LEDs is around 50,000 hours. It is important to note that LEDs behave differently at the end of their life from conventional lamps. They practically never fail but their luminous intensity decreases with age. This characteristic – known as degradation – means that the end of the life of LEDs needs to be defined: it is reached when the luminous flux has fallen to 50 percent of its original value. In practice, the long life of LEDs means they are effectively maintenance-free.

Under development: OLEDs

The rapid development of energy-efficient light generation with LEDs continues apace with OLEDs – light emitting diodes with organic semiconductors. Deposited on a paper-thin flat carrier, they open up totally new lighting possibilities, such as luminaires for room lighting spread over an entire wall or ceiling.