Selection and use of infrared lamps

1. Principle of Infrared Light Emitting Diode (LED)

The infrared light emitter is composed of an infrared light-emitting diode (LED) matrix. The infrared light emitting diode is made of a material with high infrared radiation efficiency, and a forward bias voltage is injected into the PN junction to excite infrared light. Spectral power distribution is center wavelength 830-950nm, and half-peak bandwidth is about 40nm. It is a narrow band distribution, which can be felt by ordinary CCD black and white cameras. Its biggest advantage is that it can be completely free of red bursts (using 940-950nm wavelength infrared tube) or only a faint red burst (using 850nm wavelength infrared tube); it also has the characteristics of long life.
* Red storm is visible red light

Second, the light control soft switch circuit

The infrared lamp uses a light-controlled soft switch circuit to reduce the impact of its working state transition and extend the service life of the infrared lamp.

3. Constant voltage circuit

In order to compensate for the difference between the infrared light radiation power of the infrared lamp in winter and summer, the infrared lamp uses a constant voltage and constant current circuit to stabilize the optical power of the infrared light-emitting diode, thereby improving the use effect of the infrared lamp and extending the service life.

Fourth, the choice and use of infrared lights

The most important issue in the selection of infrared lamps is the completeness of infrared lamps with cameras, lenses, protective covers, power supplies, etc. Some people have bought cameras, lenses, protective covers, power supplies, and even considered to buy infrared lights after installation. This is not correct. All equipment should be considered in the design plan, and it is regarded as an infrared low-illumination night. Design based on the monitoring system project. When considering the completeness, pay special attention to the following issues:

1. Use black and white camera or special color camera

The CCD image sensor has a wide photosensitive spectrum range. The photosensitive spectrum not only includes the visible light region, but also extends to the infrared region. With this feature, the auxiliary infrared light source can be used to illuminate the CCD image when there is no visible light at night. The imager is clearly imaged. In order to transmit color signals, ordinary color cameras separate the three primary color video signals of green, blue and red from the output signal of the CCD device, and then synthesize color TV signals. The photosensitive spectrum is only in the visible light region, so it is not suitable for infrared lamps. . Day and night dual-purpose cameras (daytime color / black and white at night) are also one of the types of infrared lights that can be used. It uses two CCDs to switch or one CCD to use digital circuit switching to achieve, but generally black and white illumination is high, or It has disadvantages such as adverse effects on color. As for the infrared low-illumination color camera, its infrared sensitivity is more than 4 times higher than that of the general camera. As the cost decreases, it will become the development trend of night vision.

2. Require low-light camera

The minimum illuminance of the camera is the scene brightness value when the brightness of the subject is low to a certain degree, and the video signal level output by the camera is lowered to a certain value. When measuring this parameter, the size of the aperture F of the lens should also be specified. Taking the lens using F1.2 as an example, when the illuminance of the scene being photographed is as low as 0.02 Lux, the amplitude of the video signal output by the camera is 50% -33% of the standard amplitude of 700mv, and the minimum illuminance of this camera is 0.02Lux / F1.2. Some camera manufacturers will clearly list the minimum illuminance value at different aperture F. When the minimum illuminance of the selected camera is higher than the requirements of the infrared lamp, the effective distance of the infrared lamp will be affected to a certain extent. It is necessary to remind users that there are two abnormalities in the minimum illuminance marked by the technical performance of cameras on the market. One is that the minimum illuminance marked by the camera manufacturer is the so-called "target surface illuminance", that is, the CCD image sensor The illuminance on the screen is about 10 times lower than the illuminance of the scene; another situation is that some camera manufacturers or distributors falsely report the minimum illuminance. At present, the most economical black and white cameras on the market, some have a minimum illumination of 0.01 to 0.02 Lux), but the actual minimum illumination is only 0.1 to 0.2Lx. If the infrared lamp used requires a minimum illumination of 0.02 Lux, it will inevitably affect the effective illumination distance of the infrared lamp, which is a point that users often overlook. If considering the fixed cost, it is recommended to buy a camera with good quality and low illumination. Although the camera with a minimum illumination of 0.02 Lux is at least twice as expensive as a camera with 0.1 to 0.2 Lux, it can save the cost of infrared lamps. The next is more cost-effective.

3. Requires camera and lens size specifications

The nominal size of the camera is becoming smaller and smaller. At present, the camera size specifications on the market are 1/2 ", 1/3" and 1/4 ". The camera size is large and the luminous flux is large. The camera size is small and the luminous flux is small. For example, the nominal effective distance of the infrared lamp is tested under the condition of 1/2 "camera. If a 1/3" or 1/4 "camera is used, the effective distance will also be affected. For example, 1/3 "camera luminous flux is only 44% of 1/2" camera luminous flux. The selection of lens size is the same as the size of the camera. In terms of the functional requirements of the camera and the lens, the camera has an automatic electronic shutter, AGC automatic gain control function, and the lens has an automatic aperture, which can adapt to large changes in day and night illumination.

4. Power supply

The power supply of the front-end equipment of the TV monitoring system should be considered in a unified design. Because the working current of the infrared tube is very sensitive to the supply voltage, and the attenuation of the DC voltage is different for different cable lengths, special attention should be paid to the use. When the distances between multiple infrared lamps and the control room are relatively large, the DC12V centralized power supply may make the infrared lamp near the control room have a high power supply voltage, and the infrared lamp far from the control room has a low power supply voltage. In addition, the deviation of the power supply voltage adjustment may cause the life of the infrared lamp with excessive voltage to be shortened or even burn out, and the infrared lamp with low voltage has insufficient emission power. Therefore, it is recommended to use AC22V power supply or one-to-one DC stabilized power supply as much as possible to ensure that the infrared radiation power of the infrared lamp can be stable and reliable. It is recommended to choose black and white cameras and high-quality lenses that are sensitive to infrared light. Pay attention to the contrast of the use environment.