Gas discharge lamps are widely used in industries, agriculture, medical and health, scientific research and other fields. In addition to being used as lighting sources, gas discharge lamps are used in photography, projection, printing, photocopying, photolithography, and chemistry. Synthesis, plastic and rubber aging, fluorescence microscope, optical oscilloscope, fluorescence analysis, ultraviolet inspection, sterilization and disinfection, medical treatment, biological cultivation, solid-state laser, etc. have a wide range of applications.
【Gas discharge lamp】Principle of gas discharge lamp Auxiliary equipment for gas discharge lamp
Principle of gas discharge lamp
The basic process of gas discharge lamp discharge light emission is divided into 3 stages:
(1) After the discharge lamp is connected to the working circuit, a stable self-sustained discharge is generated. The electrons emitted by the cathode are accelerated by the external electric field, and the electric energy is converted into the kinetic energy of free electrons;
(2) The fast-moving electron collides with the gas atom, the gas atom is excited, and the kinetic energy of the free electron is transformed into the internal energy of the gas atom;
(3) The excited gas atoms return to the ground state from the excited state, and the internal energy obtained is released in the form of light radiation. The above process is repeated, and the light continues to glow. The light radiation of the discharge lamp is related to the size of the current density, the type of gas and the level of the pressure. Certain types of gas atoms can only radiate certain spectral lines of specific wavelengths. When the pressure is low, the radiation spectrum of the discharge lamp is mainly the characteristic spectrum of the atom. When the air pressure rises, the radiation spectrum of the discharge lamp broadens and develops in the direction of long waves. When the pressure is very high, there is a strong continuous spectrum component in the radiation spectrum of the discharge lamp.
A gas discharge lamp is a lamp made by using electric current to pass gas to produce light. The energy consumed by gas discharge lamps is only 1/2-1/3 of incandescent lamps. The spectrum of a gas discharge lamp is discontinuous, and the spectrum is related to the type of gas and the discharge conditions. Changing the gas composition, pressure, cathode material and discharge current can get radiation mainly in a certain spectral range. Low-pressure mercury lamps Mercury lamps, hydrogen lamps, sodium lamps, sodium lamps, cadmium lamps, and helium lamps are commonly used light sources in spectroscopic instruments, collectively referred to as spectral lamps. For example, low-pressure mercury lamps have a radiation wavelength of 254nm and sodium lamps have a radiation wavelength of 589nm. They are often used as monochromatic light sources for photoelectric detection instruments. If the spectrum lamp is coated with a fluorescent agent, the fluorescent agent can convert the gas discharge spectrum into a longer wavelength due to the effect of light and the coating material. At present, the choice of fluorescent agent is very wide. The choice of fluorescent agent can make the gas The discharge emits a certain range of wavelengths, for example, to illuminate a fluorescent lamp.
Classification of gas discharge lamps
1. High-intensity gas discharge lamp: a discharge lamp whose luminous arc is established due to the temperature of the tube wall and the surface of the luminous tube exceeds 3W/cm2. Such as high-pressure mercury lamps, high-pressure sodium lamps, metal halide lamps, etc.
2. Low-pressure discharge lamps: fluorescent lamps (low-pressure mercury lamps), low-pressure sodium lamps, electrodeless lamps. Among them, the fluorescent lamp is a gas discharge light source that should be widely used and used in a large amount. It has the advantages of simple structure, high luminous efficiency, soft luminescence and long life. The luminous efficiency of fluorescent lamps is 4-5 times that of incandescent lamps, and the life span is 3-8 times that of incandescent lamps. It is an energy-saving light source.
Gas discharge lamp auxiliary equipment
The gas discharge lamp cannot be connected to the circuit alone. It must be connected to the circuit together with auxiliary electrical appliances such as triggers and ballasts to start and work stably.
Structure of gas discharge lamp
The basic structure of the gas discharge lamp is similar, all of which are composed of a bulb, an electrode and a discharge gas. The bulb is filled with discharge gas, and the bulb and the electrode are sealed in vacuum. The gas discharge lamp cannot be connected to the circuit alone. It must be connected to the circuit together with auxiliary electrical appliances such as triggers and ballasts to start and work stably. The starting of the discharge lamp usually requires a higher voltage than the power supply voltage, sometimes as high as several thousand volts or more than tens of thousands of volts. The above requirements can be met by using a leakage transformer or a starter. Arc discharge generally has negative volt-ampere characteristics, that is, the voltage decreases as the current increases. If the discharge lamp is connected to the power grid alone, the bulb or circuit components will be destroyed by overcurrent. The discharge lamp and ballast can be used in series to work stably. Ballasts can be resistors, inductors or capacitors. Generally, resistance ballast is used for DC power supply, inductive ballast is used for low frequency AC power supply, and capacitive ballast is used for high frequency.
Features of gas discharge lamps
The gas discharge lamp has the following characteristics:
① With high efficiency, they can convert 25-30% of the input electric energy into light output.
②Long life. The service life is as long as 10,000 hours or more than 20,000 hours.
③The radiation spectrum is selective. By selecting the appropriate luminescent material, the radiation spectrum can be concentrated on the required wavelength, and several luminescent materials can also be used at the same time to obtain a combined spectrum.
④The light output maintains good characteristics, and it can still provide 60-80% of the initial light output at the end of its life.