Vacuum fluorescent display
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A vacuum fluorescent display (VFD) is a type of display used primarily on consumer-electronics equipment such as video cassette recorders. Unlike liquid crystal displays, a VFD emits a very bright light with clear contrast.
The device consists of a cathode (filaments), anodes (phosphor) and grids encased in a glass envelope under a high vacuum condition. The cathode is made up of fine tungsten wires, coated by alkaline earth metal oxides, which emit electrons. These electrons are controlled and diffused by the grids, which are made up of thin metal.
Early on, the main disadvantage of this type of display was that it consumes "large" amounts of power (a few watts) in comparison to a simple LCD. This was considered a disadvantage for battery-operated equipment like calculators, so VFDs ended up being used primarily in equipment powered by an AC supply or heavy-duty rechargeable batteries.
During the 1980s, this display began to be used for automotive applications, especially where carmakers were dabbling with digital displays for vehicle instruments like the speedometer. A good example of these were the high-end Subaru cars made in the early 80s (referred to by Subaru enthusiasts as a digi-dash, or digital dashboard). The reason this technology is considered appropriate for electronic displays in the automotive context is because the displays are very bright.
This technology was also used from 1979 to the mid 1980s in portable electronic game units. These games featured bright, clear displays but the size of the largest vacuum tubes that could reliably be manufactured kept the size of the displays quite small, often requiring the use of magnifying Fresnel lenses. Later games had sophisticated multi-colour displays. Early games achieved colour effects using transparent filters to change the colour of the (usually green) light emitted by the phospors. High power consumption and high fragility contributed to the demise of the VFD as a videogame display, along with high manufacturing cost. LCD games could be manufactured for a fraction of the price, did not require frequent changes of expensive batteries (or AC adapters) and were much more portable. In the mid 2000s, backlit colour active-matrix LCD panels can reproduce virtually any image in full colour, compared with the fixed cell characters of the single-application VFDs of the 1980s, for a little extra cost. VFD displays are no longer used for this application.
From the mid-1980s onwards, VFDs have been used for applications requiring smaller displays with high brightness specifications though, now they are even being pushed out of these markets with the adoption of high brightness oleds.
Unlike LCDs, most VFDs continue to function normally in sub zero temperatures making them ideal for out door devices in cold climates.