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| Vacuum fluorescent display - Wikipedia Note bright green phosphors for visibility :) |
They tend to require 85 volts, so without complicated voltage inversion, not normally battery powered or portable at the pocket size like most portable consumer electronics, so it was not used on early MP3 players or similar because it would drain the battery too fast, worse than low voltage incandescent lights by comparison.
VFD when dimmed, have operating life of 200,000 hours, like low-pressure sodium lamps, my other favorite orange colored lighting technology with similar operating life & similar luminous efficiency as these garish ugly blue-white daylight colored LED's that are trending in so many applications.
6000 kelvin bluish white lighting the only thing I dislike about our 2022 Corolla Hybrid. I prefer golden yellow or orange light in the 2000k color temp that cuts through fog & rain better.
Warmer light colors are not detracted as much by water droplets, so red, orange & yellow vehicle forward illumination works better in rain, fog, snow, in dark cold early morning winter weather, in storms & during hail or icy conditions.
Our 2001 Audi A4 2.8 Quattro has 4200k HID lighting, but a tasty optical system that produces off angle warm pinkish light & pinkish purple, white the cool white light thrown forward by precision optics offers enough green light to provide exceptional contrast detection for the human eyes, since the retinal peak spectral sensitivity 520nm green laser light, or our eyes are most sensitive to lime green colors, neon lime green, that's why almost all safety vests & safety signs transitioned from neon orange to neon lime green.
In light, 4200K cool white contains the greenest light from Xenon HID lamps like the ones used in the aforementioned Audi A.
I like Xenon HID more than LED for vehicle forward illumination, and projector headlights with optics that concentrate & focus the light to reduce glare for oncoming drivers while also lighting up the roadway better so I can see where I am going more easily in dark conditions, like when I am driving to work at 5am in the morning during the winter when it's very dark at this time, or coming home at 7pm at night during the winter when it's also dark at that time.
Lets explore how the VFD works for fun :)
A VFD operates on the principle of cathodoluminescence, roughly similar to a cathode ray tube, but operating at much lower voltages. Each tube in a VFD has a phosphor-coated carbon anode that is bombarded by electrons emitted from the cathode filament.
In fact, each tube in a VFD is a triode vacuum tube because it also has a mesh control grid.
VFD emits very bright light with high contrast and can support display elements of various colors. Standard illumination figures for VFDs are around 640 cd/m2 with high-brightness VFDs operating at 4,000 cd/m2, and experimental units as high as 35,000 cd/m2 depending on the drive voltage and its timing.
The choice of color (which determines the nature of the phosphor) and display brightness significantly affect the lifetime of the tubes, which can range from as low as 1,500 hours for a vivid red VFD to 30,000 hours for the more common green ones.
Cadmium was commonly used in the phosphors of VFDs in the past, but the current RoHS-compliant VFDs have eliminated this metal from their construction, using instead phosphors consisting of a matrix of alkaline earth and very small amounts of group III metals, doped with very small amounts of rare earth metals.
VFDs can display seven-segment numerals, multi-segment alpha-numeric characters or can be made in a dot-matrix to display different alphanumeric characters and symbols. In practice, there is little limit to the shape of the image that can be displayed: it depends solely on the shape of phosphor on the anode(s).
The first VFD was the single indication DM160 by Philips in 1959.
The first multi-segment VFD was a 1967 Japanese single-digit, seven-segment device.
In the late 1980s hundreds of millions of units were made yearly
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