Types
Lamps are divided into families based on the pressure of gas in the bulb, below. A second distinction used is whether the cathode is heated:
- Hot-cathode lamps have electrodes which operate at a high temperature, which during operation are heated by the arc current in the lamp. The heat knocks electrons out of the electrodes by thermionic emission, which helps maintain the arc. In many types the electrodes consist of electrical filaments made of fine wire, which are heated by a separate current at startup, to get the arc started.
- Cold-cathode lamps have electrodes which operate at room temperature. To start conduction in the lamp a high enough voltage (the striking voltage) must be applied to ionize the gas, so these lamps require higher voltage to start.
Read more about this topic: Gas Discharge Lamps
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