Working principle of high pressure sodium lamp

Answer:

When the bulb is started, the arc tube arcing between the electrodes at both ends, due to the high temperature of arc tube to liquid sodium mercury vapor evaporation as mercury vapor and sodium vapor emitted from the cathode to anode electrons in the movement process, impact discharge atomic material to obtain energy, produce ionization or excitation, and then by the excitation return to the ground state; or by the ionized into an excited state to the ground state, then an infinite loop, at this time, the release of excess energy in the form of light radiation, will produce light. High pressure sodium vapor pressure in the discharge of material is very high, namely sodium atom density, sodium atom collision between electron and frequent, the resonance radiation broadening of spectral lines, there radiation in the visible spectrum, so the color is better than that of low pressure sodium lamp high pressure sodium lamp. High pressure sodium lamp is a kind of high intensity gas discharge bulb. Due to the negative resistance characteristics of gas discharge lamp, if the bulb alone received the power grid, the working state is unstable, with the discharge process continues, it will lead to the current in the circuit infinite rise, until the last lamp or circuit parts are overcurrent burned.

The fluctuation will supply voltage caused by lamp light and electric parameters; if the power supply voltage will cause the rise of bulb current increases, the arc tube cold end temperature increase, mercury and sodium vapor pressure increased, with the increase of the working voltage, the power of the bulb, causing the lamp life is greatly reduced; on the other hand, the power supply voltage is reduced, the light is not working properly and the decrease of luminous efficiency, may cause the bulb does not start or extinguish. Therefore, the requirements of customers in the use of light bulbs, the power supply voltage fluctuations should not be too large, generally required in the range of +6% to -8% range.

After the high pressure sodium lamp is started, the mercury vapor and xenon low pressure discharge at the initial stage. At this time, the lamp voltage is very low, a large current discharge process; with the continuation of the arc temperature gradually increased, mercury and sodium vapor pressure by the discharge tube cold end temperature, when the discharge tube cold end temperature reaches stable discharge will tend to be stable, light flux, voltage, current and power it is in normal working condition. Under normal working conditions, the whole start-up process takes about 10 minutes.

Although it is not like a resistive capacitive ballast ballast consumes great power, low temperature rise, the power frequency is low, the capacitor charging time, will produce the pulse peak current, causing great damage to the electrode, flashing lights, affect the service life of the bulb; working in high frequency circuit, the voltage fluctuation can reach the ideal state, the ideal the ballast. Inductive ballast loss, impedance stability, impedance of speed deviation is small, long service life, light stability than resistive ballast, ballast and supporting the use of high-pressure sodium lamp for inductive ballast. Its shortcomings are cumbersome and high prices. In addition, electronic ballasts have begun to appear, the price is expensive, reliability can not match with high-pressure sodium lamp, except for special occasions, it is rarely used in general. Therefore, the high-pressure sodium lamp must be connected in series with the bulb specifications corresponding to the ballast before use. The lighting circuit of high voltage sodium lamp is a nonlinear circuit with low power factor, so the compensation capacitor is considered on the network to improve the power factor of the network.

Volt ampere characteristicAs with other gas discharge bulbs, high pressure sodium lamp works in the arc discharge state, and the volt ampere characteristic curve is negative slope, that is, the bulb current rises, while the bulb voltage decreases. In the constant power supply conditions, in order to ensure the stable operation of lighting circuits, circuit elements must be in series with positive resistance characteristics to balance the negative resistance characteristics of the stable working current, the element is called ballast or limiter. Resistors, capacitors, inductors, etc are all finite current action. The resistive ballast has the advantages of small size, low price, and supporting the use of high pressure sodium lamp will occur is difficult to start work, have a very high heat resistance, heat dissipation need space, large power consumption, will make the total decline in the efficiency of lighting circuit. It is generally used in DC circuit, the use of lights in the AC circuit has obvious flicker phenomenon.