[ Huaqiang Security Network News
The development direction of video surveillance lies in outdoor. The development direction of outdoor surveillance lies in night vision. The development direction of night vision lies in infrared technology. This trend is more and more obvious. In the field of infrared night vision, Chinese companies have already taken the lead in the world. However, this is an emerging industry. A large number of inferior products are flooding the market, which affects people's trust in infrared night vision products. This paper deals with common technical problems in infrared night vision monitoring, and hopes to provide valuable reference for engineers and users to further understand infrared night vision monitoring.
So does the infrared light really have a fixed illumination distance? Does infrared night vision monitoring only involve infrared light technology? Numerous facts prove that the answer is no. In fact, as far as the infrared lamp itself is concerned, there is absolutely no fixed illumination distance. It is unscientific to mark the distance of the infrared lamp in isolation. There are also professional professionals and manufacturers who are unaware that infrared lamps need to have excellent cameras and excellent infrared lenses in order to achieve the desired illumination. The most frequently heard statement is that an infrared sensor camera with a value of 0.001Lux or more is required, preferably black and white; a special infrared lens is required, and the infrared transmittance is more than 95%. The problem is that any worker engaged in professional optical research and manufacturing knows that these so-called lenses with an infrared transmission rate of more than 95% really have to achieve more than 95% of the infrared transmission. The rate is more difficult.
Some manufacturers have been able to create a red-violet-free infrared light as a technical issue to promote, as if there is a red storm is low technology, no red storm is high technology. In fact, whether or not there is a red storm is only a matter of choice, not a technical issue. Light with a wavelength of more than 700 nm is called infrared light, and infrared light of 900 nm or more is basically no red storm. The shorter the wavelength, the stronger the red storm and the higher the infrared sensitivity. There are two mainstream infrared lamps on the market. One is slightly red, the wavelength is around 850 nm, and the other is red-free. The wavelength is around 940 nm. The same camera, the sensitivity at 850nm wavelength is 10 times better than the sensitivity at 940nm. Therefore, the 850nm infrared light with a slight red storm has higher efficiency and should be the first choice for infrared night vision monitoring.
The life of the camera can be more than 10 years. Can the life of the infrared lamp reach this level? To answer this question correctly, we must first understand the current principle of infrared light. At present, infrared lamps mainly have three modes: 1, halogen lamps, 2, multi-chip LEDs, 3, single-chip LEDs. Halogen lamp is a more traditional technology, with high energy consumption, large heat generation and short service life. Due to its inefficient use, it is estimated to gradually fade out of the market.
Multi-chip LEDs are also available in two versions, one with 4 to 8 chips and the other with arrayed illuminators containing 10 to 30 chips. Why do you need multiple chips? The theory from some manufacturers is: the infrared light irradiation distance is not enough because the energy is not enough, more chips are brought together, of course, the energy is large, taking it for granted that the irradiation distance is farther. Of course, longer distances require more energy, but instead of infrared light emitting more infrared light, the camera can receive more effective reflected infrared light. Multi-chip LEDs have no illuminating focus due to their inherent disadvantages in structure, optical systems are unreasonable, and useful light efficiencies are relatively low (of course, several times stronger than halogen lamps), and their advantages are not fully realized, such as array LEDs, current Up to 1000mA or more, basically just a penny coin size, heat dissipation becomes a problem.
What LEDs are most afraid of is high heat, not bad. At the same time, the production requirements of multi-chip LEDs are very strict, and each chip can't have a difference in performance. Otherwise, if the chip is broken, the whole machine will be finished. Overall, the lifetime of multi-chip LEDs is not enough compared to single-chip LEDs.
The single-chip LED production process is simple, the quality is easy to guarantee, the heat generation is low, and the optical system is reasonable. It is an ideal device for infrared lamps, and the theoretical service life can reach more than 100,000 hours. So, is it true that all single-chip LED lights have a good life? In fact, this is far from the case. There are many reasons for this. For example, some LED chips are very low in level and impurities are excessive; some production processes are not related to leakage; some are used in super power, rated at 20mA, but use 50mA or more; some have no protection circuit, or circuit Unreasonable design, these will cause the single-chip LED infrared lamp to break.
In order to ensure the life of the infrared lamp, we must first select a high-grade LED chip. High-grade chips have high power, good consistency, high luminous efficiency, and low heat generation. High-grade LEDs are much better than ordinary LEDs, and the price is very expensive. Secondly, the optical system should be designed reasonably, the illumination should be uniform, the utilization rate should be high, and the heat dissipation should be fast. Third, we must strictly control the working voltage. The LED is very sensitive to voltage, the LED dies will burn off when the voltage is slightly higher, and the luminosity will be greatly reduced when the voltage is slightly lower. It is best to match the high-quality switching power supply. The AC input voltage is preferably well regulated from 170 volts to 270 volts to suit the harsh power supply environment. Fourth, the input power line is preferably made to withstand high/low temperature, soft and resistant to bending. There is an infrared lamp produced by a manufacturer. The input power line can be used normally at a low temperature of 60 degrees and a high temperature of 250 degrees.
Is the infrared light the better the angle of view? Whether manufacturers or engineers take it for granted, they believe that the larger the angle of view of the infrared light, the greater the room for the lens. The wide-angle lens does not have a "flashlight" phenomenon. Therefore, everyone is desperately saying how big the angle of view of their infrared lamps is. This seemingly plausible argument is actually very unscientific.
First of all, there is a waste phenomenon when using a large-angle infrared light with a small-angle lens. For example, the illumination angle of an infrared lamp is 80 degrees (equivalent to the angle of a f3.5mm lens). If a lens of f35mm is used, a considerable part of the light will be outside the field of view of the lens, that is, part of the infrared light is wasted. In general, the angle of view of the infrared light should be consistent with the angle of view of the lens, and the effect is optimal. The emission angle of the infrared lamp of Changchun Yida is expressed by the focal length of the lens. For example, SK-4.2W-16 infrared lamp, 4.2W indicates that the rated power of the lamp is 4.2 watts; 16 indicates the emission angle of the lamp and f16mm The lens angle is the same, and the two can be matched.
Secondly, the larger the angle of emission of the infrared light, the better the picture will be. In some cases, if the angle of the infrared light is too large, it will affect the imaging. For example, the corridor, because of its "small and long" characteristics, if the emission angle of the infrared light is too large, the imaging of the near edge will be too bright, forming a "light curtain" phenomenon; the far center is invisible, only a white phenomenon. Therefore, the infrared light in the corridor should be one-half or one-third of the lens angle.
Third, you can use the "lighting" technology, two narrow-angle infrared lights to match and adjust the position, you can achieve the effect of wide-angle lights, the market's "night hawk" series infrared night vision system, is the use of "lighting" Technology has achieved both telephoto and wide angle. Under the same power conditions, the "lighting" technology can double the range of action.
In general, the problem of the angle of emission of infrared lamps is both a matter of choice and a matter of technology. For lenses of different focal lengths, infrared lamps that are compatible with the emission angle should be selected. The emission angle of the infrared lamp should not be larger than the angle of view of the lens under any conditions, but in a narrow environment, it should use an infrared lamp that is smaller or even one-third larger than the lens angle. The narrow-angle infrared light can be matched to achieve the desired wide-angle effect.
The relative aperture determines the light-passing capability of the lens. The amount of light passing through the lens with a relative aperture of F1.0 is four times that of the lens with a relative aperture of F2.0. The same camera and infrared light, respectively, with the above two types of lenses, the infrared distance can be doubled.
In the infrared monitoring, the large-aperture lens is 4 to 10 times better than the conventional ordinary lens. It is reasonable to say that it should become an essential accessory for infrared night vision monitoring, but it is costly and technically difficult.
Due to well-known reasons, a large number of lenses with false F-values â€‹â€‹on the market, especially zoom lenses, only short-focus and non-standard telephoto are misleading engineering companies, which makes it impossible for users to distinguish who is selling real goods. Users are advised to purchase lenses from professional large manufacturers.
Due to the different wavelengths of visible light and infrared light, the imaging focus is not on a plane, resulting in clear images under visible light conditions during the day, and blurred under nighttime infrared light conditions, or clear images under nighttime infrared light conditions, and blurred images under visible light conditions during the day. It can be solved in three ways. First, the use of auto-focus integrated camera; second, the use of IR-specific focus does not shift the lens; third, the use of professional adjustment tools under the existing lens conditions, can also achieve focus non-offset.
All black and white cameras can sense infrared light. Infrared light is a kind of stray light for color cameras, which will reduce the sharpness and color reproduction of color cameras. The color camera filters prevent infrared rays from participating in imaging. There are two ways to make a color camera sense infrared. First, switch the filter to block the infrared light from entering under visible light conditions; remove the filter in the absence of visible light and let the infrared light enter. The image obtained by this scheme is good in quality, but the cost is high, and the switching mechanism causes The failure rate is increased. Second, opening a specific infrared channel on the filter allows infrared light of the same wavelength as the infrared light to come in. This method does not increase the cost, but the color reproduction is slightly worse.
Camera sensitivity is a core part of infrared night vision monitoring. The better the sensitivity, the stronger the ability to sense infrared light. Of course, the better the sensitivity, the more expensive the camera is.
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