What Is a Green Cathode?

Geisha A. Legazpi

A green cathode is a cold cathode device used for lighting. Cold cathode devices are used to emit ions into a gas-filled tube with phosphor coatings that are responsible for the green color. Other colors for the cold cathode include white and red. The green cold cathode comes with a separate power supply that generates voltage high enough to drive the green cathode light tube. Voltage in power outlet is around 110 volts alternating current (VAC), while the power supply generates about 650 VAC.

Man holding computer
Man holding computer

While the green cathode is used with alternating current (AC), some other types of cathodes are used with direct current (DC). Unlike the green cathode, the negative cathode is used in active electronic devices called vacuum tubes. Positive cathode devices refer to the electrolyte polarity in batteries. The cathode material in rechargeable batteries is able to retain its chemical properties, even with numerous charge and discharge cycles.

Hot cathode devices are also used for fluorescent tube lighting to compensate for low-voltage operation. These devices have starters that temporarily heat up the cathodes so that current across the tube can begin to flow. Once current has started flowing, there is indirect heating of the cathode, and the ionization and subsequent illumination of the phosphor coating are sustained.

Another type of hot cathode is used in the cathode ray tube, and early cathode ray tubes were the first versions of the wide-screen cathode ray tubes that were very popular as screens for television (TV) sets. The cathode of the cathode ray tube located at the rear of the TV is at a low voltage, while the anode with a high voltage in tens of thousands of volts is closely coupled to the TV screen. When electrons from the cathode are released toward the anode and into the screen, there is illumination in the phosphor of the screen. Color TV sets use red-green-blue (RGB) phosphor coated as a fine matrix on the inside of the TV screen. With the right circuitry, full-color image reproduction, in-sync with broadcast program, is displayed on screen.

Green cathode lighting is very popular because it is very efficient, uses less electricity, and generates less heat. These make green cathode and other cold cathode lighting devices suitable to be used near or inside sensitive equipment. Advances in power supply technology result in very economical generation of high voltage required to supply power to devices such as the green cathode.

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