No special function of the camera to camera at night, often because of the scene illumination is too low to work effectively, and in order to realize the vision, now mostly adopts the infrared imaging technology.

Infrared imaging technology is divided into passive infrared camera technology and active infrared camera technology two kinds. Passive infrared camera technology is the use of any material above absolute zero infrared emission, infrared light from the human body and the engine is stronger, infrared light is very weak, from other objects using special infrared camera can realize monitoring at night. But, this kind of special infrared cameras are expensive, and can not reflect the status of the surrounding environment, so little in the night vision system used. Night vision system is frequently used in active infrared imaging technology, which adopts the infrared radiation, infrared people see not, "lighting" landscape and environment, application of ordinary low illumination color during the day and night automatically become black and white and black and white camera camera or infrared low illumination color camera, feel the environment reflected infrared night vision.

The following will be based on the principle, types and characteristics of infrared lamp is introduced as follows.

Infrared principle is introduced

The wavelength of light is an electromagnetic wave, which range from a few nanometers (1 nm = 10 to 9) to 1 millimeter (mm). Visible to the human eye is just one part of a, we call it the visible light, the wavelength of visible light is 380 nm to 780 nm range, the visible wavelength from long to short is divided into red, orange, yellow, green, green, blue, purple light, called ultraviolet wavelength shorter than purple light, the wavelength than red light, long known as infrared light.

Ordinary CCD can experience the spectral characteristics of light black and white camera is shown in figure 1, the figure can be seen, it can not only feel the visible light, but also can feel infrared light. This is using ordinary CCD, black and white camera with infrared lamp can compare economy to realize the basic principle of night vision. The spectral characteristics and ordinary color video camera is not feel the infrared light, therefore cannot be used for night vision.

Infrared lamp principle and characteristics

Infrared lamp according to the mechanism of infrared radiation is divided into solid light-emitting semiconductor (infrared emission diode), infrared lamp and thermal infrared lamp. Its principle and characteristics are as follows:

1. The infrared emission diode (LED) lamp

Consists of infrared emission diode matrix luminous body. Infrared emitting diode by infrared radiation of high efficiency materials commonly used gallium arsenide (GaAs) made of p-n junction, plus forward biased toward the p-n junction injection current stimulate infrared light. Spectral power distribution as the center wavelength of 830 ~ 950 nm, about 40 nm half peak bandwidth, as shown in figure 2. It is a narrow distribution, for the common CCD camera can feel the scope of the black and white. Its biggest advantage is can completely without red storm, (in 940 ~ 950 nm wavelength infrared tube) or only a faint red binge (red critical to have a visible red light), and long service life.

In general, the infrared radiation power is proportional to the positive working current, but near to the maximum rating of forward current, the temperature of the device for current heat consumption to rise, make the light emitting power decrease. Infrared diode working current is too small, will affect the radiation power of the play, but the working current overshoot affect its life, and even make the infrared diode burned.

Infrared emission diode volt-ampere characteristics are very similar with normal silicon diode. When the voltage across the positive threshold voltage (0.8 V) current to flow, but also a very steep curve, showed that the working current is very sensitive to the working voltage. Therefore requires accurate and stable working voltage, otherwise influencing the full play of the radiation power and reliability.

Infrared lamp especially long-distance infrared lamp, heat loss is the problem that should pay special attention to during the design and selection.

General maximum radiation intensity in front of the optical axis, and decreases with the increase of the radiation direction and optical axis Angle. 50% of the radiation intensity for maximum Angle is called half Angle of radiation intensity. Different models of infrared light-emitting diodes encapsulation technology of radiation Angle is different.

2. The basic principle and characteristics of thermal infrared lamp

Thermal radiation phenomenon is very common, all objects in the low temperature of thermal radiation is infrared light, so the human eye cannot be directly observed. When heated to 500 degrees or so, dark red visible light is produced, along with the temperature rise, the light becomes more bright and white. In the thermal radiation light source by heating filament to maintain its temperature, for radiation to continue. To maintain a certain temperature from the outside to provide energy and reduced as a result of radiation energy balance.

Radiator under different heating temperature, the peak wavelength of radiation is different, the spectral energy distribution are different.

According to the above principle, the infrared light bulb made of special design and process, the infrared component of up to 92 ~ 95%. Overseas production technical for the infrared light bulb: 100 ~ 375 w power; The power supply voltage of 230 ~ 250 v. The service life of 2000 ~ 5000 hours, radiation Angle of 60 ~ 80 degrees. Figure 7 shows the spectral power distribution, spectral range is very wide. General feeling of black and white camera spectrum frequency range is very wide, and the infrared light bulb can generally be made larger and powerful irradiation Angle, thus can be used for long-distance infrared lamp, that is the greatest advantage of it. Its biggest shortcoming consists of optical elements, namely has red storm, and short service life, if work 10 hours a day, can only be used for more than a year 5000 hours, and considering the heat dissipation is not enough, and short service life. And for the customer, change the light bulb is the trouble and unhappy things.

Made many efforts to overcome the thermal radiation lamp faults in the first is the development and application of the infrared filter high-pass toughened glass. The long wavelength, the smaller the red storm, even can reach devoid of red storm, however, lower the efficiency of the infrared light, infrared lamp heating is high. The wavelength of infrared glass according to user requirements for red storm discretion to choose, in general, the same effective irradiation distance, red critical requirements higher, the higher the cost. Infrared after toughened glass, can tolerate the change of the thermal shock, internally infrared light bulbs due to filter out the part of the visible light into heat, the temperature will be very high, under the raid of external cold wind and rain and snow, cold snap without damage. In order to improve thermal infrared lamp life, adopted light-controlled switch circuit, to reduce the working time; Using the variable voltage regulator, rectifier circuit, to give full play to its luminous power and improve the service life of lamp; But more important is to consider the filament of cold resistance is very small, such as 100 w infrared light bulb, A filament is 529 Ω thermal resistance, then the working current of only 0.4348 A, only 36 Ω and cold resistance, infrared lamp instantaneous power supply is connected to A transient power of 1470 w, 6.39 the moment filament load overload of dozens of times, it has very big effect to the filament life. People of the filament protection circuit, believe that the working life of the lamp bulb will be multiplied. In addition, also increases the delay switch circuit in case of light interference environment.