Do they exist? Florescent tubes work by creating a plasm within the tube which generates UV. The UV in turn strikes the phospor coating on the tube surface generating visible white light. I was wondering if a line of UV LED's could line the inside of a florescent tube to generate the needed UV. It might make for a direct replace of florescent tubes. Your ideas?
Do they exist? Florescent tubes work by creating a plasm within the tube which generates UV. The UV in turn strikes the phospor coating on the tube surface generating visible white light. I was wondering if a line of UV LED's could line the inside of a florescent tube to generate the needed UV. It might make for a direct replace of florescent tubes. Your ideas?
Yes they exist at near UV wavelengths, about 330 nm was the shortest the last time I looked. The efficiency of these LEDs are not comparable to the super bright LEDs at 405 nm. In addition, I doubt that the efficiency of the phosphors in standard fluorescent lights, which are optimized for excitation by the 250 nm mercury line, would work very well with the much longer wavelengths.
Bret Cannon
This already exists.
It's called a "white LED".
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
The usual white LEDs have a phosphor (occaisionally a phosphor combo) irradiated by a blue LED die rather than a UV one. In the usual practice, some of the blue light makes it through the phosphor to mix with the yellowish light produced by the phosphor in order to make "white light".
As for UV LEDs:
The common low power ones include ones with output in general ballpark when wavelength is ~395 nm or ~400-405 nm (nominally borderline or deep visible violet). There are also a few with output power in the ~1 mW ballpark with peak wavelength around 350-380 nm. Life expectancy of these are better when the LED die is not encapsulated in touching-the-die plastic material such as epoxy or a casting resin.
There are shorter wavelength ones, with wavelengths ranging from low
300's to ~250-260 nm, but output power tends to be milliwatt ballpark and the cost tends to be an order of magnitude or more higher than is the case of LEDs with peak wavelength 350 nm or more. This situation gets worse as wavelength decreases.-- - Don Klipstein (don@misty.com)
For lighting needs that are directed, where LEDs seem more competitive, there already exist products like these:
Jon
nt
I guess you don't fly much. The first "security" person you meet is the guy that checks to see if the name on your driver's license matches the name on the ticket. He/she also uses a UV flashlight to see if your DL is valid.
I have a UV flashlight for rock hunting. Good for finding scorpions too (they glow green). I built a multi-CCFT UV light years ago before the UV leads came out. The old CCFTs were really bright, but if you have 30 or so UV Leds, they work too.
Most stores had been slipping your money under CCFT UV bulbs for years, but most people never noticed. If you go to CES, there is a row of money verification vendors.
nt
I "think" thats what they are doing with the new line of lamps. This one shows a little like I wanted to see.
-60/
By using a few UV's in series the voltage drop would not be so wasted.
greg
Yes, they do.
There is a lack of UV LEDs with good efficiency at wavelengths much below 365 nm, and efficiency of UV LEDs is maximized at 380-plus nm. Most fluorescent lamp phosphors do not respond well to wavelengths near or longer than 350 nm. Fluorescent lamp phosphors are intended to work mainly from 254 nm, secondarily from 185 nm, and it's a bonus if they work from 310 nm.
I am aware of a blue-glowing phosphor component in triphosphor and compact fluorescent lamps generally 3500-plus Kelvin that works at longer UV and deep visible violet wavelengths. I am also aware of a bluish-green-glowing phosphor component used in some CFLs 3500K and higher and in GE "Reveal" CFLs, which works at longer UV wavelengths. In my experience, these are the main exceptions to the general rule that fluorescent lamp phosphors tend to not work well or significantly from wavelengths around and over 350 nm.
The usual white LEDs are actually largely fluorescent lamps. They have blue-emitting chips coated with a phosphor that absorbs most of the blue light, but passes through some of the blue light. The blue light that is absorbed is used to produce fluorescence of a yellowish broad or broadish band from typically mid-green to mid-red. The bandwidth is greater for higher-color-rendering-index ones, less for lower-color-rendering-index ones.
For at least a couple to probably a few years already, ledsmagazine.com has mentioned fluorescent lamp style shape/size/bases lamps that have LEDs in them.
Lately, better white LEDs are getting more efficient than fluorescent lamps, at least when driven less aggressively.
-- - Don Klipstein (don@misty.com)
There are LEDs that have peak wavelength as low as 260 or maybe 250 nm, but ones of wavelength in the low 300's nm and less are inefficient and expensive. Also, last time I checked, they produced a couple to a few milliwatts at most, and mostly not much more than 1 milliwatt below 300 nm.
LEDs with peak wavelength in the low 300's or less nm also tend to be quite expensive.
-- - Don Klipstein (don@misty.com)
White LEDs already are fluorescent lamps. In fact, the larger lamps are arrays of blue or violet LEDs with a single fluorescent diffuser lens over them. The lens is chosen to match the color of existing lighting.
You can buy LED arrays meant for directly replacing fluorescent tubes. They're intended for cold locations where tubes perform poorly, like supermarket freezers
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