The principle, performance and application of infrared light emitting diode
Infrared light emitting diodes (IR LEDs) are devices that have the advantages of small size, long lifespan, and stable performance. Therefore, they are widely used as active infrared light sources in infrared night vision cameras, effectively making up for the shortcomings of nighttime monitoring. IR LEDs have good concealment and do not interfere with the lives of nearby residents.
The performance of infrared devices directly affects the night vision effect of cameras. In actual use, not only should high-performance devices be selected, but also suitable devices should be chosen and used in conjunction with appropriate cooling methods to achieve the best results.
The principle of IR LEDs is to inject carriers into the PN junction by forward bias, and the carriers recombine in the active region and release excess energy in the form of infrared radiation. The wavelength distribution of near-infrared light emitting devices is 0.76 to 3 microns, with a half-bandwidth of about 40nm, and belongs to narrowband distribution. In practical applications, 850nm IR LEDs are generally used as night vision illumination sources for infrared cameras, while 940nm IR LEDs and longer wavelength devices are mainly used in light control or remote control.
The emission power of IR LEDs is expressed in irradiance. Generally, the infrared radiation power is proportional to the forward operating current, but when the current approaches the maximum rated value, the temperature of the device rises due to the thermal consumption of the current, which not only reduces the radiation power of the device but also affects its lifespan, and even causes it to burn out. Therefore, the thermal consumption of IR LEDs is a problem to be noted in design and use.
The working current of IR LEDs is very sensitive to the working voltage. When forward conduction occurs, the current increases exponentially with the increase of the voltage. The maximum radiation intensity of IR LEDs is generally in front of the optical axis and decreases with the increase of the angle between the radiation direction and the optical axis. The angle at which the radiation intensity is 50% of the maximum value is called the half-intensity radiation angle, and the radiation angles of IR LEDs with different packaging processes and models are different.
In night vision cameras, the application of IR devices is not only related to the infrared light source but also to the selection of CCD lenses and usage conditions. Therefore, it is recommended to choose suitable devices for use. Generally, for the same power emitting devices, the smaller the emitting angle, the longer the irradiation distance, and the corresponding irradiation range will be reduced. Under the same angle, the higher the power of IR LEDs, the farther the irradiation distance.
With the development of LED packaging technology, IR LEDs have made significant progress. Currently, IR LEDs are mainly divided into ordinary through-hole IR LEDs, high-power IR LEDs, and multi-chip array IR LEDs. Ordinary through-hole IR LEDs are mainly used for small-range and short-distance infrared irradiation. In practical applications, multiple devices need to be connected together to achieve better irradiation effects. The advantage of high-power IR LEDs is that they have high radiation power, and small-angle devices have a far irradiation range. However, due to the large input power, the heat generation is relatively large, and appropriate heat conduction design and matching heat dissipation structures are needed. The multi-chip array IR LEDs combine multiple chips together, have high energy, and have a relatively long irradiation distance. However, the complex manufacturing process and difficulty in improving the yield rate have limited their development.
Watt Smith
Collaborator & Editor
Hello! My name is Watt Smith working on Chipdatas. I write and share relevant articles on electronic components category.
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