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Vacuum fluorescent displays (VFDs) are high-contrast displays mostly used in consumer electronic devices, such as audio/video equipment for the home or vehicles. The displays are typically colored green and can display numerals, dot matrix patterns or alphanumeric characters. They are bright and perform well in all light conditions including full sunlight. Vacuum fluorescent displays have various advantages such as liquid crystal display (LCD) compatibility and can be considered as suitable replacements for organic light emitting diode (OLED) and liquid crystal display modules.
A vacuum fluorescent display is comprised of a filament, insulation layer, anode electrode, wiring pattern and grid. Filament is the cathode for the vacuum fluorescent display and usually is made of alkaline-coated tungsten wires, which help in emitting light. The cathode is heated by an external source to emit the free thermal electrons and the grid controls the electrons. In order to achieve non-light emission, the electrons from the filament are either blocked by the grid or by the negative potential anode. Similarly, for light emission, the electrons from the filament accelerate to the positively charged anode and the phosphor on the anode emits luminous radiation due to the excitation of the electrons.
Vacuum fluorescent displays make use of advantages found in both light-emitting diodes and liquid crystal displays. One prominent feature is the high level of brightness with clear contrast. It is generally considered a more attractive and versatile alternative to liquid crystal displays due to the low cost involved. Vacuum fluorescent displays are usually green, but are available in other colors as well. They have a wide operating temperature range and can also function in subzero temperatures, unlike liquid crystal displays. They also offer high contrast ratio and wide viewing angle.
One of the considerable drawbacks of vacuum fluorescent displays is that they cannot display anything other than the preset combinations of patterns, words, letters or numerals and hence are not suited for large screens. They also consume more power than liquid crystal displays and so are not considered suitable for portable devices.
Vacuum fluorescent displays still remain a popular choice for robust and simple displays in electronic appliances.