The basic process of discharge luminescence of gas disc […]
The basic process of discharge luminescence of gas discharge lamps can be divided into three stages:
(1) When the discharge lamp is connected to the working circuit, it produces a stable self-sustaining discharge. The electrons emitted from the cathode are accelerated by the external electric field, and the electric energy is transformed into the kinetic energy of the free electrons.
(2) Fast moving electrons collide with gas atoms, gas atoms are excited, and the kinetic energy of free electrons is converted into the internal energy of gas atoms.
(3) The stimulated gas atoms return to the ground state from the excited state and release the obtained internal energy in the form of light radiation. When the above process is repeated, the lamp will continue to glow. The light radiation of discharge lamp is related to the current density, gas type and air pressure. A certain kind of gas atom can only radiate certain wavelength spectrum. At low atmospheric pressure, the emission spectrum of the discharge lamp is mainly the characteristic spectrum of the atom. When the pressure rises, the radiation spectrum of discharge lamp broadens and develops towards long wave direction. When the air pressure is very high, the continuous spectral component is strong in the radiation spectrum of the discharge lamp.
Gas discharge lamp is a kind of lamp which uses electric current to produce luminous phenomenon through gas. The energy consumption of gas discharge lamp is only 1/2-1/3 of that of incandescent lamp. The spectrum of gas discharge lamp is discontinuous. The spectrum is related to the type of gas and discharge conditions. By changing the composition of gas, pressure, cathode material and discharge current, radiation can be obtained mainly in a certain spectral range. Low pressure mercury lamp, hydrogen lamp, sodium lamp, cadmium lamp and helium lamp are commonly used light sources in spectral instruments, collectively called spectral lamp. For example, low-pressure mercury lamp low-pressure mercury lamp radiation wavelength 254 nm, sodium lamp radiation wavelength 589 nm, they are often used as a monochrome light source for photoelectric detection instruments. If the spectral lamp is coated with fluorescent agent, because of the effect of light and coating material, fluorescent agent can convert the gas discharge spectrum line into longer wavelength. At present, the choice of fluorescent agent is very wide. By choosing fluorescent agent, the gas discharge can emit a certain range of wavelength, such as fluorescent lamp.
Classification of Gas Discharge Lamps
1. High Intensity Gas Discharge Lamp: A discharge lamp with a surface load of more than 3W/cm2 is built up because of the wall temperature. Such as high pressure mercury lamp, high pressure sodium lamp, metal halide lamp, etc.
2. Low pressure discharge lamp: fluorescent lamp (low pressure mercury lamp), low pressure sodium lamp and electrodeless lamp. Among them, fluorescent lamp is the most widely used gas discharge light source. It has the advantages of simple structure, high light efficiency, soft luminescence and long life. The luminous efficiency of fluorescent lamp is 4-5 times of that of incandescent lamp, and its lifetime is 3-8 times of that of incandescent lamp. It is an efficient and energy-saving light source.
Gas Discharge Lamp Auxiliary Equipment
Gas discharge lamp can not be connected to the circuit alone. It must be connected to the circuit together with flip-flops, ballasts and other auxiliary appliances in order to start and work stably.
Structure of Gas Discharge Lamp
The basic structure of gas discharge lamp is much the same, which is composed of bubble shell, electrode and discharge gas. The bubble shell is filled with discharge gas, and the vacuum gas seal is used between the bubble shell and the electrode. Gas discharge lamp can not be connected to the circuit alone. It must be connected to the circuit together with flip-flops, ballasts and other auxiliary appliances in order to start and work stably. The starting of discharge lamps usually requires a higher voltage than the power supply voltage, sometimes up to several thousand volts or more. The magnetic flux leakage transformer or starter can meet the above requirements. Arc discharge generally has negative volt-ampere characteristics, that is, the voltage decreases with the increase of current. If the discharge lamp is connected to the power grid separately, the bulb or circuit components will be destroyed by overcurrent. The discharge lamp and ballast can work stably only when they are connected in series. Ballasts can be resistors, inductors or capacitors. Usually, resistance ballast is used in DC power supply, inductance ballast is used in low frequency AC power supply and capacitance ballast is used in high frequency power supply.
Characteristics of Gas Discharge Lamp
Gas discharge lamps have the following characteristics:
They can convert 25-30% of the input electric energy into optical output.
(2) Long life. The service life is as long as 10,000 hours or more.
(3) Radiation spectrum has selectivity. By choosing appropriate luminescent substances, the radiation spectrum can be focused on the required wavelength, and several luminescent substances can be used at the same time in order to obtain the best combination spectrum.
(4) Optical output maintains good performance, and can still provide 60-80% of the initial optical output at the end of life.
