Current LED technology has asserted itself. The many advantages ensure the advance of LED lighting in all areas of life. But how do LEDs and LED lamps work at all? This guide brings light into the darkness and shows you the structure and functionality of LEDs and LED lamps. This will give you a good understanding of current lighting technology.
How does an LED work?
The abbreviation LED stands for light-emitting diode. This means as much as light-emitting semiconductor component. The basic functionality is simple, because LEDs consist of only a few components. This includes:
- Bond wire
- LED chip
- Reflective cavity
- Epoxy lens
The LED chip sits in a small reflective cavity on the cathode. A gold wire, also known as a bonding wire, creates the current flow between the anode and cathode. A lens made of plastic or epoxy resin holds all parts together and ensures good light distribution at the same time. The LED chip is a semiconductor crystal and consists of two layers of differently doped semiconductor material.
In one semiconductor layer there is an excess of positive charge carriers. In the other layer the negative charge carriers are in the majority. If the anode and cathode are supplied with voltage, an electron flow occurs between the semiconductor layers. As a result, energy is released, resulting in small flashes of light. The LED emits photons, which we then perceive as visible light.
The LED chip has an edge length of only about one millimeter and emits quasi point-shaped light. It is only through the reflective cavity that the light is directed into the upper half of the light emitting diode. Depending on its composition, the plastic lens distributes the light in the room accordingly. In addition, the plastic composite makes the LED insensitive to shocks and vibrations.
The wavelength of the emitted light can be determined very precisely by doping the semiconductor material. Depending on the application, LEDs can be produced with different light colors and color temperatures. Due to the narrow wavelength range, no other radiation in the infrared or UV range is generated.
Further LED Types
The basic LED functionality and its structure has been described before. There are still different subtypes of light emitting diodes. SMD LED’s and COB LED’s are mainly used for LED illuminants and luminaires.
SMD LED Structure
The abbreviation SMD stands for surface mounted device. SMD LED’s can be mounted directly on the printed circuit board in the light source. With this design, the housing also serves as a heat sink for the LED chip. This allows good heat dissipation, which reduces the chip temperature. Due to the good cooling, the LED can be operated with a higher current, which allows a high efficiency to be achieved.
SMD LED’s are also quite compact. For this reason, they are often used in large numbers in a single light source. For example, in lamps with a large beam angle, several LEDs are usually arranged in a circle. By combining different LED types it is also possible to achieve certain color spectra.
COB LED Structure
The COB LED is a further development of the SMD variant. The abbreviation COB stands for chip on board. Here, the LED chip is attached directly to the printed circuit board with thermal adhesive. Due to the direct contact between the semiconductor and the board, the power dissipation can be dissipated even better than with the SMD version. This further improves cooling, which further increases efficiency.
Thanks to the ultra-compact design, COB LED’s can be used to produce any imaginable shape of LED luminaire. Many futuristic lamp designs have only become possible through COB technology. On the other hand, a high chip density allows a high light output to be generated in the smallest of spaces. This makes it possible to produce very bright LED spotlights, among other things.
How do LED lights work?
The functionality of an LED lamp has become much more complex compared to conventional light sources. In addition to one or more light-emitting diodes, an LED lamp also has other components. These include:
- LED driver
- Power supply
The basic structure and functionality of an LED has already been described in the previous paragraphs. In most retrofit LED light sources mainly SMD LED’s are used. In modern LED luminaires, COB technology is used to a large extent. This allows modern luminaires to be designed which were not possible with the standard forms of retrofit lamps.
Generate operating voltage
LED lamps are available for 110V mains voltage as well as for 12V or 24V low voltage. LED lamps for mains voltage have a built-in power supply unit, which generates a low voltage from the 110V. Low voltage LED lamps do not have an integrated power supply, but must be connected to an external LED transformer.
LED driver as power source
The semiconductor chip in the LED must be operated at its correct operating point. Only then can a high degree of efficiency and constant brightness be achieved. This would be difficult to achieve with a pure voltage source due to quality scattering in LED mass production. For this reason, the LED is operated at a constant current source called an LED driver.
The LED driver, especially for LED lamps in the low-cost range, sometimes only consists of a resistor, which causes the current to adjust. In many high voltage lamps power supply and driver are often combined in one circuit, which is also called LED driver.
White light through light mixing
White light is usually required for lighting purposes. However, LED’s cannot generate this light directly. One way of generating white light is to mix three LED’s with the colors red, green and blue. By controlling it with different brightness, this combination makes it possible to set any other RGB color in addition to white. At the same time, this variant is also the most expensive.
In most LED lamps, white light is therefore produced in a different way. Blue LED chips with a phosphor layer are used here. Blue in combination with the yellowish phosphor layer produces a light mixture that appears as white light. This manufacturing process also determines the color temperature, such as cold white, natural white or warm white.
Optics for light distribution
The optics of an LED lamp provide the desired light distribution. Many lamps contain diffusion lenses or diffusion discs. This allows the beam angle to be adjusted and homogeneous radiation to be achieved. By combining the LED arrangement in the lamp body with the optics, almost any desired lamp shape can be produced.
You now have an overview of the structure and function of LED’s and LED lights. The complexity has increased compared to the old light sources. However, the advantages and possibilities of LED technology literally put the old light sources in the shade.