In electroluminescent radiators, the electrical energy produces visible radiation. One of the characteristic aspects of light emitting diodes, LEDs, is their narrow banded spectrum, while their advantages include a compact shape, high colour density, a long life, and low power consumption in led lighting technology
Light emitting diodes, LEDs, have extremely long life, impact resistance and low energy consumption. When dimmed, the light colour remains constant. When connected to the mains, they require control gear to ensure the correct operating current. The point light source provides for precise light control while the plastic encapsulation of the diode acts as protection and lens. The output of the LED decreases with increasing temperature. Consequently, good heat dissipation is important for smooth operation. Direct solar radiation should be avoided so too installation near other sources of heat. With an average rated life of 50,000 hours, LEDs are suitable for long operating times. As they start instantly and react directly to control, they are ideal for quick, dynamic light scenes. The development of LEDs currently focuses on more compact shapes, a higher luminous flux, and better luminous efficacy as well as a more economical production process. A further goal is the reduction of production-related colour deviations. Manufacturers sort LEDs by luminous flux and dominant wavelength and give them a bin code and a rating. This sorting of LEDs is called binning.
LEDs are semiconductor diodes that belong to the group of electroluminescent radiators. The light is generated by recombining charge-carrier pairs in a semiconductor with an appropriate energy band gap. LEDs produce narrow- band radiation. The colour temperature remains constant as the light intensity decreases. LEDs used for lighting do not produce UV or IR radiation.
When voltage is applied to the cathode and the anode, the LED emits light from the barrier layer. Electrons change their energy level and through recombination release photons at the pn-junction. The wavelength of the light produced depends on the semiconductor materials in led lighting technology.
Coloured LEDs
LEDs produce a narrow banded spectral range. The dominant wavelength determines the colour locus of the LED. Compared to coloured fluorescent lamps, LEDs have a higher colour density. The composition of the semiconductor material determines the light spectrum emitted. Differently coloured LEDs of the same connected load produce different levels of luminous flux.
White LED
White light cannot be produced with semiconductor materials. Consequently, white light is currently generated using two methods: RGB mixing or luminescence conversion. The colour rendition of white LEDs currently approximates a colour rendition index Ra of 90. The light colours available include warm white, neutral white, and daylight white LEDs of 2500K to 8000K.
RGB LED
By combining three light diodes with the light colours red, green and blue (RGB), the light colours can be mixed to produce a wide range of colours, including white. The red, green and blue LEDs can be controlled to adjust their different light intensities
T-type LED
The standard T-type LED has a plastic housing measuring 3-5mm for the wired LED. The shape of the lens determines the light emission angle. As a light source with a low luminous flux it is used as an orientation or a signal luminaire.
SMD LED
With the “Surface Mounted Device” (SMD) shape, the component is glued directly to the circuit board and the contacts are soldered.
COB LED
The “Chip on Board” (COB) technology places the chip directly on a circuit board without its own housing. The anode and cathode contact can be made using thin wires. The chip is sealed to protect it.
High-power LED
High-power led lighting technology are LEDs with a power consumption of over 1W. This includes both SMD and COB LEDs. The key factor is their special construction that ensures very low thermal resistance between the chip and the circuit board. High-power LEDs are usually used on metal core circuit boards requiring special thermal management in the luminaire.
References :
- Erco Lighting guide