ฟลูออเรสเซนต์

Jump to navigation Jump to search This article ฟลูออเรสเซนต์ about light sources and indicators. For cold cathode ion sources, see Ion source.

This article needs additional citations for verification. A cold cathode is a cathode that is not electrically heated by a filament. A cold-cathode vacuum tube does not rely on external heating of an electrode to provide thermionic emission of electrons. Early cold-cathode devices included the Geissler tube and Plucker tube, and early cathode ray tubes. Neon lamps are used both to produce light as indicators and for special-purpose illumination, and also as circuit elements displaying negative resistance. The flash tube is a cold-cathode device filled with xenon gas, used to produce an intense short pulse of light for photography or to act as a stroboscope to examine the motion of moving parts.

Cold-cathode fluorescent lamps are used for backlighting of LCDs, for example computer monitors and television screens. 20 mm in diameter and operating on a current of 120 to 240 milliamperes. This larger-diameter tubing is often used for interior alcove and general lighting. The cathode is the negative electrode.

Both electrodes alternate between acting as an anode and a cathode when these devices run with alternating current. A cold cathode is distinguished from a hot cathode that is heated to induce thermionic emission of electrons. Discharge tubes with hot cathodes have an envelope filled with low-pressure gas and containing two electrodes. An electron that leaves the cathode will collide with neutral gas molecules. The collision may just excite the molecule, but sometimes it will knock an electron free to create a positive ion. Another mechanism to generate free electrons from a cold metallic surface is field electron emission. Cold cathodes sometimes have a rare-earth coating to enhance electron emission.