What does a light-emitting diode do
This is how LED lamps work - a simple explanation of LED technology
The current LED technology has prevailed. 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 article sheds light on the darkness and shows you the structure and function of LEDs and LED lamps. This will give you a good understanding of current lighting technology.
Table of Contents
How does an LED work?
The abbreviation LED stands for in English light-emitting diode. Translated it means something like light-emitting semiconductor component. The basic functionality is easy to explain, because LEDs consist of only a few components. This includes:
- Bond wire
- LED chip
- Reflector tray
- Plastic lens
The LED chip sits in a small reflector tub on the cathode. A gold wire, which is also known as a bond wire, creates the flow of current between the anode and cathode. A lens made of plastic or epoxy resin holds all parts together and at the same time ensures good light distribution. 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, a flow of electrons occurs between the semiconductor layers. As a result, energy is released, creating 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 point-like light. Only through the reflector trough is the light directed into the upper half of the light-emitting diode. The plastic lens ensures appropriate light distribution in the room, depending on its properties. In addition, the plastic compound makes the LED insensitive to shocks and vibrations.
The wavelength of the emitted light can be determined very precisely by doping the semiconductor material. This means that LEDs can be specifically manufactured with different light colors and color temperatures depending on the application. Due to the narrow range of the wavelength, no other radiation in the infrared or UV range is generated.
Other LED types
The basic LED functionality and its structure have been described above. There are also various subspecies of light-emitting diodes. SMD LEDs and COB LEDs are predominantly used for LED lamps and lights.
SMD LED structure
The abbreviation SMD stands for surface mounted device. SMD LEDs can be attached directly to the circuit board in the lamp. With this design, the housing also serves as a heat sink for the LED chip. This enables good heat dissipation, which lowers the chip temperature. Due to the good cooling, the LED can be operated with a higher current, which enables a high level of efficiency to be achieved.
SMD LEDs are also quite compact. This is why these are often built into a light source in large numbers. For example, several LEDs are usually arranged in a circle in lamps with a large beam angle. 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 circuit board with thermal adhesive. Due to the direct contact between the semiconductor and the board, the power loss can be derived even better than with the SMD version. This further improves the cooling, which further increases the efficiency.
Thanks to the ultra-compact design, COB LEDs can be used to produce all imaginable forms of LED luminaires. Many futuristic lamp designs have only become possible thanks to COB technology. On the other hand, a high density of chips enables high light output to be generated in a very small space. This allows, among other things, very bright LED spotlights to be produced.
How does an LED lamp 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 has other components. This includes:
- LED (s)
- LED driver
- power adapter
The basic structure and functionality of an LED has already been described in the previous paragraphs. Most of the retrofit LED light sources use mostly SMD LEDs. In modern LED lights, COB technology is used for the most part. This allows modern lights to be designed, which were not possible with the standard forms of retrofit lamps.
Generate operating voltage
LED lamps are available for 230 volt mains voltage as well as for 12 or 24 volt low voltage. LED lamps for mains voltage have a built-in power supply, which generates a low voltage from the 230 volts. Low-voltage LED lamps do not have an integrated power supply unit, but must be connected to an external LED transformer.
LED driver as a 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 do with a pure voltage source due to quality variations in LED mass production. For this reason, the light-emitting diode is operated on a constant current source called an LED driver.
Especially with LED lamps in the low-cost range, the LED driver sometimes only consists of a resistor, which sets the current. In many high-voltage lamps, the power supply unit and driver are often combined in one circuit, which is also known as an LED ballast.
White light through light mixing
We usually need white light for lighting purposes. However, this cannot be generated directly by LEDs. One way to generate white light is to mix three LEDs with the colors red, green and blue. By controlling with different brightness, this combination can be used 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 generated in a different way. Blue LED chips with a phosphor layer are used here. Blue in combination with the yellowish phosphor layer creates a mixture of light that appears as white light. During this manufacturing process, the color temperature, such as cold white, neutral white or warm white, is also determined.
Optics for light distribution
The optics of an LED lamp ensure the desired light distribution. Many lamps contain diffusing lenses or diffusion discs. The radiation angle can be adjusted and a homogeneous radiation can be achieved. By combining the LED arrangement in the lamp body in conjunction with the optics, almost any desired lamp shape can be produced.
You now have an overview of the structure and functionality of LEDs and LED lamps. Compared to the old light sources, the complexity has increased. However, the advantages and possibilities of LED technology literally put the old light sources in the shade.
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