Category Archives: LEDs Effect

  Application of Infrared IR LED in Infrared Camera With the increasing demand for night vision monitoring in security video surveillance system engineering, infrared cameras have entered the mainstream market of cameras, and sales are increasing day by day. Problems in the application of infrared night vision technology are gradually exposed. In fact, night vision technology is a photoelectric technology that realizes night observation by means of photoelectric imaging devices. It includes two types of low-light night vision and infrared night vision: low-light night vision technology is a night vision technology with an image intensifier tube, which actually enhances the faint target image illuminated by night skylight for observation photoelectric imaging technology. Here we mainly talk about active infrared night vision technology, which is a night vision technology that implements observation by actively illuminating and using the infrared light reflected by the target to reflect the infrared source. The corresponding equipment is an active infrared night vision device, and the actual core is an infrared camera. The infrared light source, the camera composed of the non-direct-view photoelectric imaging device CCD or CMOS image sensor as the core, and the lens required for the imaging screen are the three major factors that dominate the night surveillance effect of the infrared camera. Selection of infrared light source Infrared light is an invisible light with a wavelength greater than 780nm. Generally, there are the following three methods for generating such invisible light. ①. Directly use the infrared light emitted by incandescent lamp or xenon lamp. That is, install visible light filters on these two lamps to filter out visible light and only let invisible infrared rays emit; ②. Use infrared light-emitting diodes (LEDs) or LED arrays to generate infrared light. This device generates infrared light through the recombination of electrons and holes in a gallium arsenide (GaAs) semiconductor; ③. Using infrared laser diode LED can also be used as infrared light source. However, it needs to excite or pump electrons in a lower energy state to a higher energy state, and maintain stimulated emission of infrared light through a large number of particle distribution reversals and resonance. The first type of light source is a thermal infrared light source. Its biggest advantage is that it can be made into a relatively large power and a large irradiation angle, so the irradiation distance is long. Its biggest disadvantage is that it contains visible light components, that is, there is a red burst, and its service life is short. If it works 10 hours a day, it can only be used for 5000 hours for more than a year. If the heat dissipation is not enough, the service life is even shorter. In order to improve the service life of the thermal radiation infrared lamp, it is necessary to use a light control switch circuit to reduce its working time. In addition, a delay switch circuit is added to prevent the interference of ambient light. The second is an infrared lamp composed of a semiconductor gallium arsenide light-emitting diode array, especially the array-type integrated light-emitting chip LEDArray that is now developed and produced using new technology. The optical output of one LED-Array has reached 800mw-1000mw, and it has become a replacement product of ordinary LEDs. The half-power angle of the LED-Array is 10-120° (variable angle). Since the LED-Array is a highly integrated LED, and its volume is only the size of a penny, it can evenly illuminate the entire space indoors, and its lifespan is 50,000 hours. It was originally used on aviation aircraft. In recent years, due to the development of the civilian night surveillance market, LED-Array has gradually entered the civilian market and has become an ideal choice for high-quality night surveillance. Although infrared LED and LED-Array have eliminated thermal infrared light sources, for the monitoring of ultra-long-distance scenes over 1km, infrared LED light sources should still be selected. Because semiconductor lasers have the characteristics of higher brightness and stronger directionality than LEDs. Generally, the following points should be paid attention to when choosing an infrared light source. There should be a margin in the distance selection of infrared lamps When choosing an infrared lamp, pay special attention to the gap between the nominal distance and the actual irradiation distance. Because the nominal viewing distance of some manufacturers is often too large, it is necessary to conduct actual tests when selecting the irradiation distance of infrared lamps, and to leave sufficient margin to make the illuminance of the observed scene reliable. A light source driven by a steady current source should be selected Because LED is a current-driven device, its luminous brightness and power are proportional to the driving current, not the voltage. Therefore, in order to keep the luminous intensity constant, a light source driven by a steady current source must be selected. Choose a light source with good heat dissipation Because luminous tubes have heat and heat dissipation problems, especially light sources with high power and long distances generate a lot of heat, so it is necessary to choose a light source with good heat dissipation to ensure stable and reliable work. It is necessary to choose an infrared light source with a power supply circuit with a light-controlled switch automatic control circuit and separated from the light board Because the power supply circuit of the infrared lamp is not separated from the lamp board, the heat generated by the light-emitting tube will affect the performance of the components of the power supply circuit, resulting in unstable light emission of the light-emitting tube. With this light-controlled switch circuit, the infrared The lights are off during the day and on at night. Infrared lamps should be selected according to the monitoring distance Because the infrared light-emitting diode LED can be installed on the lens, it can be used with a sensitive infrared camera, or directly installed on the casing around the interface between the camera and the lens. Obviously, these two types of devices have fewer infrared LEDs, and their irradiation distance is definitely not as far as that of a single infrared LED lamp. Generally, if it is more than 50m, it is better to choose a separate infrared lamp. In addition, LED is mostly used for night vision lighting of monitoring scenes with a distance of more than 1km, but the beam of LED is thin and strong. In order to make the infrared beam illuminate a certain range of scenes, use Sometimes it is necessary to expand the beam through a beam expander lens. Second, the choice of camera At present, there are two types of photosensitive devices in cameras: CMOS and CCD. Like the CCD, the CMOS image sensor chip also responds to infrared light waves, but its sensitivity in the range of 890-980nm is much higher than that of the CCD image sensor chip, and the attenuation gradient is slower as the wavelength increases. With the rapid development of CMOS image chips, their noise signals have been further reduced, and star-level CMOS cameras have also appeared on the market. Therefore, it is not necessarily limited to the choice of CCD cameras, but can be selected by making full use of their respective advantages. In general, the selection points of infrared cameras are as follows. A low-illuminance camera should be selected, and its illumination requirements are generally ≤0.02Lux Some camera manufacturers or sellers falsely report the minimum illuminance, which greatly reduces the effective distance of night vision, so it is best to test it in detail. Intensified cameras such as moonlight level and starlight level can work in very dark conditions, but some places with small reflective coefficients still cannot meet the requirements, such as deserts, green lands, forest areas, etc. In this case, it is necessary to use a low-light night vision camera that is directly coupled by a high-performance image intensifier and a CCIR black and white CCD through a fiber panel and a light cone. In short, the lower the illuminance, the better. Since it is not yet standardized, the minimum illuminance claimed by the manufacturer cannot be trusted. It is better to test it under practical conditions. Usually, the illuminance requirement is generally ≤0.02Lux. The larger the size of the selected infrared camera image sensor, the better Because 1/4CCD cannot be used for the effective distance of infrared night vision above 15m, because the luminous flux of 1/4CCD is only 50% of 1/3CCD. The larger the size of the CCD, the larger the received luminous flux; the smaller the size of the CCD, the less the received luminous flux. Therefore, choose 1/2 of the CCD for the night vision camera, and 1/3 of the CCD can be tested if it is feasible, but you must not choose 1/4 of it. Infrared cameras must have automatic electronic shutter and automatic gain control (AGC) functions Because of these functions, the signal can be adjusted to a better state to meet the observation effect. Choose a CMOS ultra-miniature camera for concealed occasions Because low power consumption, high integration, and small size can only be achieved by CMOS image sensors, it can be made into a CMOS camera with the size of a shirt button or a suit button. Coupled with the miniaturization of the corresponding infrared light source and the introduction of high-efficiency batteries, the third eye will be ubiquitous. In this way, with a pair of night vision glasses and a hat equipped with an infrared light source and a CMOS ultra-miniature camera, the night will be like the day. Clearly, this will change the face of our entire social life. Choose the supporting small power supply for the camera The selection of the power supply of the camera should pay attention to the following two points Select a regulated power supply. Because the mains AC220V is unstable, if only one AC-to-DC 12V transformer is selected and the voltage is not stabilized, the circuit in the camera will work unstable, so that the camera will not work stably, and the required performance will not meet the requirements; It is better to choose a small power supply that is more than twice the current of the camera. If the current of the camera is 200mA or 250mA, generally 500mA is sufficient. If it is too large, such as 1A for 1 camera, the volume will be too large and the price will be too expensive; if it is too small, such as equal to the current of the camera, it may generate heat (due to long continuous working time) and affect reliability and working life. Third, the choice of lens, etc. The camera lens is the key equipment of the infrared camera. Its quality (indicator) directly affects the imaging effect of the system. Therefore, the selection of the lens is not only related to the quality of the system, but also related to the project cost. Therefore, pay attention to the following points when choosing a lens: It is best to choose an infrared lens Because of the ordinary optical lens, the infrared light reflected by the object back to the lens cannot be effectively focused on the CCD target surface. At this time, the infrared night vision effect will be greatly reduced, so it is best to use an infrared lens. Especially for color-to-black cameras, if the infrared lens is not used, the focal plane of the day and night monitoring cannot be consistent, so that the day and night images cannot be kept clear. The imaging size of the selected lens should preferably be consistent with the size of the image sensor in the camera The imaging size of the selected lens should be consistent with the size of the image sensor in the camera. If the size of the image sensor is 1/2″, the imaging size of the lens must be 1/2″. When the imaging size of the lens is larger than the size of the photosensitive surface of the camera, the imaging will not be affected, but the actual imaging field of view