At this stage, energy conservation has become a rigid requirement, not an option, and some of them need to adopt environmentally friendly green methods to achieve energy conservation. For lighting, we can easily imagine the impact of global lighting increasing efficiency by 10%, but increase it by 1000%? Recently, high-efficiency light-emitting diodes ( LEDs ) have been able to achieve this efficiency improvement, and have been able to replace the products used at this stage with good performance and high reliability. This article has four parts. The first part focuses on the physical structure of LEDs, the range of illumination, efficiency, LED driving and applications.
Physical analysis
Physically, LEDs are similar to pn junction diodes. As a pn junction, when a positive voltage is applied between the anode (p region) and the cathode (n region), electrons and holes move toward the cross section. Once the electrons and holes recombine will release energy, the physical properties of the pn material determine the form of energy release. As for the standard diodes used in discrete circuits, they can release energy either without radiation or in visible light. freed. For an LED, the wavelength at which it emits light (ie, the color of the light) is determined by the forbidden band width characteristic of the pn junction material. To improve performance, LED materials must have a low reverse breakdown voltage, which is a low forbidden band width.
colour
In the late 1960s, red LEDs were first used commercially, but the light emitted at the time was very weak. Despite this deficiency, red LEDs are widely used in seven-segment displays. Due to advances in materials science, commercially available LEDs can now emit multiple shades of light, and some of them can blind your eyes if you stare directly at them.
Blue LEDs have been widely used a few years ago. Mixing the light produced by the blue, green and red LEDs produces white light. This white light-emitting technology provides a wide color gamut with good dynamic tuning characteristics and excellent color rendering (CRI). High-end backlight applications. Producing white light with blue LEDs and phosphors is simpler and more economical, and it converts some of the blue light into yellow light. Yellow light can mimic the red and green light that the eye feels, so blue and yellow light can produce white light. This scheme can provide good color rendering performance, but the white light generated by this method suffers from the inconsistency of the coloring temperature due to the difference in the manufacturing process and the difference in the phosphor thickness.
Figure 1: LED color chart for several basic colors
effectiveness
High efficiency is a term for LED light sources. When lighting is mentioned, efficiency is defined as the light produced by unit power, so in the metric system, it is measured in lumens per watt. Some LED products have recently been introduced with an efficiency of up to 150 lm/W, compared to 15 lm/W for incandescent lamps and 70 lm/W for fluorescent lamps. So will LEDs replace incandescent and fluorescent lights in the near future? It is possible, but unfortunately some of the LED's efficiency data is only stuck in the specification. The problem is that a significant portion of the light produced by the LED is reflected back to the LED chip on the surface of the package material. For this fact, the LED itself is powerless. This partially reflected light may be absorbed by the semiconductor material and converted into heat.
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