What is the principle and application of infrared lamp

1、 Overview

IR night vision and white light

In the TV monitoring system project, infrared lamps were rarely used in the past. In recent years, they have not only been used in important departments such as Treasury, oil depot, armory, library, cultural relics department and prison, but also in general monitoring systems. Even the TV monitoring project in residential areas has also applied infrared lamps. This shows that people’s requirements for TV monitoring system engineering are becoming more and more standardized and higher. It requires not only daytime and nighttime visible light lighting monitoring, but also nighttime covert monitoring.

With the development of TV monitoring system engineering technology, the number of users who buy infrared lamps has increased rapidly, and many problems have also emerged. For example, a user bought more than ten infrared lamps and said that none of them were bright. After inquiry, he learned that he used ordinary color cameras, while ordinary color cameras do not feel infrared light; Some users say that your infrared lamp can not reach the nominal irradiation distance. After understanding, they lack the understanding of the matching requirements of the infrared lamp on the camera, lens, protective cover and power supply system. In the design of TV monitoring project, they do not consider it as an infrared low illumination low illumination holiday night vision system project; Some users think they know about the infrared lamp and increase the power supply voltage of the DC12V infrared lamp to increase the irradiation power of the infrared lamp, or use an unstable DC power supply to supply power to the DC12V infrared lamp, causing the infrared lamp to burn; Some users report that they have selected cameras according to the illuminance required by the infrared lamps, but they can not obtain clear images within the nominal irradiation distance of the infrared lamps, and they do not know that the minimum illuminance given by some camera manufacturers has moisture, or they intentionally or unintentionally use the vague concept of minimum illuminance, replacing the scene illuminance with the so-called target illuminance; In addition, some users do not fully understand the factors affecting the acquisition of clear images other than the camera illumination, such as the nominal size of the camera and the lens, the lens aperture F, the focal length f, and the functional requirements of the camera. We believe that it is beneficial to introduce the principle, selection and application methods of some infrared lamps to TV monitoring equipment dealers, engineers and users.

The method to realize night vision can use conventional visible light illumination. However, this method can not be hidden, but more exposed the monitoring target (there are problems of disturbing residents in residential areas). Hidden night vision monitoring is currently using infrared camera technology. Infrared camera technology is divided into passive infrared camera technology and active infrared camera technology. Passive infrared camera technology is to use any substance to emit infrared light above absolute zero. The infrared light emitted by human body and heat engine is strong, and the infrared light emitted by other objects is weak. Night monitoring can be realized by using special infrared camera. However, this special infrared camera is expensive and cannot reflect the surrounding environment, so it is not used in the night vision system. Active infrared camera technology is often used in night vision systems, that is, infrared radiation “illumination” is used to generate infrared light that is invisible to human eyes but can be captured by ordinary cameras, and radiate “illumination” scenery and environment. Ordinary low illuminance black-and-white camera, daytime color automatic black-and-white camera or infrared low illuminance color camera are used to feel the infrared light reflected from the surrounding environment to realize night vision.

2、 Principle and characteristics of infrared lamp

Light is an electromagnetic wave with a wavelength range from several nanometers (1nm = 10-9m) to about 1 millimeter (mm). What the human eye can see is only part of it. We call it visible light. The wavelength range of visible light is 380nm ~ 780nm. The wavelength of visible light is divided into red, orange, yellow, green, blue, blue and violet light from long to short. The wavelength shorter than violet light is called ultraviolet light, and the wavelength longer than infrared light is called infrared light.

Ordinary CCD black-and-white camera can feel the spectral characteristics of light, it can not only feel visible light, but also infrared light. This is the basic principle that night vision can be realized economically by using ordinary CCD black-and-white camera and infrared lamp. However, the spectral characteristics of ordinary color cameras can not sense infrared light, so they cannot be used for night vision.

According to its infrared radiation mechanism, infrared lamps are divided into semiconductor solid-state light emitting (infrared emitting diode) infrared lamps and thermal radiation infrared lamps. Its principle and characteristics are introduced as follows:

  1. Principle and characteristics of infrared emitting diode (LED) infrared lamp
IR night vision

A luminescent body composed of an infrared light emitting diode matrix. The infrared emitting diode is made of a material with high infrared radiation efficiency (commonly used gallium arsenide GaAs) to make a PN junction, and a forward bias voltage is applied to inject current into the PN junction to excite infrared light. The spectral power distribution is the center wavelength of 830-950nm, and the half peak bandwidth is about 40nm. It is a narrow-band distribution, which can be perceived by ordinary CCD black-and-white cameras. Its biggest advantage is that it can be completely free of red burst (940-950nm wavelength infrared tube) or only weak red burst (red burst is visible red light) and long life.

Irradiance for emission power of infrared light emitting diodes μ W / m2. Generally speaking, the infrared radiation power is directly proportional to the forward working current. However, when the maximum rated value of the forward current is approached, the temperature of the device rises due to the heat consumption of the current, and the light emission power decreases. If the current of the infrared diode is too small, it will affect its radiation power. However, if the working current is too large, it will affect its life and even burn the infrared diode.

When the voltage exceeds the forward threshold voltage (about 0.8V), the current starts to flow, and it is a very steep curve, indicating that the working current is very sensitive to the working voltage. Therefore, the working voltage is required to be accurate and stable, otherwise the radiation power and its reliability will be affected. The radiation power will decrease with the increase of the ambient temperature (including the increase of the ambient temperature generated by its own heating). Heat consumption of infrared lamps, especially long-distance infrared lamps, should be paid attention to in design and selection.

The maximum radiation intensity of the infrared diode is generally in front of the optical axis, and decreases with the increase of the angle between the radiation direction and the optical axis. The angle at which the radiation intensity is 50% of the maximum value is called the half intensity radiation angle.