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The principle of infrared light and its characteristics

Light is an electromagnetic wave, its wavelength range from a few nanometers (1nm = 10-9m) to about 1 mm (mm). Visible to the human eye is only part of it, we call it visible light, visible light wavelength range of 380nm ~ 780nm, visible light wavelength from long to short into red, orange, yellow, green, green, blue, blue, purple light, wavelengths shorter than the violet light called ultraviolet light, wavelengths longer than the infrared light called infrared light.
　　Ordinary CCD black and white camera can feel the spectral characteristics of light, it can not only feel the visible light, and can feel the infrared light. This is the use of ordinary CCD black and white camera, with infrared light can be more economical to achieve the basic principle of night vision. The spectral characteristics of ordinary color cameras can not feel the infrared light, and therefore can not be used for night vision.
　　Infrared light according to its infrared light radiation mechanism is divided into semiconductor solid light-emitting (infrared emission diode) infrared lamps and thermal radiation infrared lamps of two kinds. Their principles and characteristics we introduce as follows.
　　

1. infrared emission diode (LED) infrared lamp principle and characteristics
　　Infrared light-emitting diode (LED) infrared lamps are composed of a matrix of infrared light-emitting diodes. Infrared emission diodes by the infrared radiation efficiency of the material (commonly used GaAs GaAs) made of PN junction, plus forward bias to inject current into the PN junction to excite infrared light. Spectral power distribution for the center wavelength 830 ~ 950nm, half-peak bandwidth of about 40nm, it is a narrow-band distribution, for ordinary CCD black and white camera can feel the range. Its biggest advantage is that it can be completely red burst-free, (using 940 ~ 950nm wavelength infrared tube) or only a weak red burst (red burst for visible red light) and long life.
　　Infrared light-emitting diodes emitted power with irradiance μW/m2 said. In general, its infrared radiation power is proportional to the forward operating current, but in close proximity to the maximum rating of the forward current, the temperature of the device rises due to the thermal dissipation of current, so that the light emission power decreases. Infrared diode current is too small, will affect its radiation power play, but the working current is too large will affect its life, and even make the infrared diode burned.
　　When the voltage crosses the positive threshold voltage (about 0.8V or so) the current begins to flow, and is a very steep and straight curve, indicating that its working current is very sensitive to the working voltage. Therefore, the working voltage is required to be accurate and stable, otherwise it affects the play of radiation power and its reliability. Radiation power with the rise in ambient temperature (including its own heat generated by the rise in ambient temperature) will make its radiation power decline. Infrared lamps, especially long-range infrared lamps, thermal dissipation is the design and selection should pay attention to the problem.
　　Infrared diode’s maximum radiation intensity is generally directly in front of the optical axis, and decreases with the increase in the radiation direction and the angle of the optical axis. Radiation intensity is 50% of the maximum angle called half-intensity radiation angle. Different packaging process models of infrared light-emitting diode radiation angle varies.
　　2. the basic principle of thermal radiation infrared lamp and its characteristics
　　Thermal radiation phenomenon is extremely common, the object at a lower temperature when the thermal radiation is all infrared light, so the human eye can not be directly observed. When heated to about 500 degrees, only when the visible light will be produced dark red, as the temperature rises, the light becomes brighter and whiter. In the thermal radiation light source by heating the filament to maintain its temperature for radiation to continue continuously. The energy provided from the outside to maintain a certain temperature is balanced with the reduced energy due to radiation.
　　Radiation body in different heating temperature, the peak wavelength of radiation is different, and its spectral energy distribution is also different.
　　According to the above principle, the infrared light bulb made by special design and process, its infrared light composition up to 92-95%. Foreign production of this infrared light bulb technical performance for:
　　Power 100 ~ 375W; supply voltage 230 ~ 250V; service life of 5000 hours, radiation angle 60 ~ 80 degrees.
　　

Ordinary black and white cameras feel the spectral frequency range is also very wide, and infrared light bulbs can generally be made of relatively large power and large irradiation angle, so it can be used for long-distance infrared light, which is its greatest advantage. Its biggest shortcoming is the inclusion of visible light components, that is, there are red storms, and the use of short life, if you work 10 hours a day, 5000 hours can only be used for more than a year, considering the heat dissipation is not enough, life is also short. And for customers, replacing the light bulb is a trouble and unpleasant thing.
　　Many efforts have been made to overcome the shortcomings of thermal radiation infrared lamps, the first is the development and application of high-pass infrared filtering tempered glass. The longer the wavelength, the smaller the red burst, and even up to no red burst, but the lower the efficiency of infrared light, the higher the heat of the infrared lamp. Infrared glass wavelengths can be selected according to the user’s requirements for red burst, generally speaking, the same effective irradiation distance, the higher the requirements for red burst, the higher the cost. Infrared glass after tempering, can withstand rapid cold and heat changes in the internal infrared bulb due to visible light filtered part of the conversion to generate heat, the temperature will be very high, the external cold wind and rain and snow raids, rapid cold without damage. To improve the life of the thermal radiation infrared lamp, the use of light-controlled switching circuit to reduce its working time; using a variable voltage regulator rectifier circuit, so that its luminous power to give full play and improve the life of the infrared lamp; and more importantly, consider the filament cold resistance is very small, such as 100W infrared bulb, the filament thermal resistance of 529Ω, the working current at this time is only 0.4348A, while the cold resistance is only 36 Ω, the infrared lamp on the power instantly for 6.39A instantaneous power to 1470W, the instantaneous filament load overload of dozens of times, which has a very significant impact on the filament life. People developed the filament protection circuit, I believe the infrared lamp bulb working life will increase exponentially. In addition, a time delay switch circuit has been added to prevent light interference from the environment.