>> UV LEDs producing even a few mW of power have until recently cost hundre=
ds of dollars.

> Have I been duped or has there been a recent breakthrough that makes thes=
e kind of UV LEDs cheap?

Price goes up, and power output goes down, as the peak wavelength decreases=
..
395-405nm LEDs are cheap and pretty bright, but they're definitely closer t=
o "violet" than ultraviolet.  A 12mW output LED is about $1 from LEDSupply.=
com
375-385nm starts to be the point where emissions are less "visible."  A 6.8=
mW output 375nm device is about $3.
LEDSupply also has a 750uW 361nm LED for about $4, and a 200uW 351nm LED fo=
r about $20.
(LEDSupply is not the cheapest vendor, but I'd rate them a reasonably trust=
worthy, and they have a range of wavelengths to compare, all in one place.)
(keep in mind that a fluorescent "Black Light Bulb" peaks at about 370nm, a=
nd "short wave" UV doesn't start to about 315nm)

Several of the cheap UV (~400nm) LEDs I bought via eBay had a very short li=
fetime :-(
(That was a number of years ago.  But the point is that this is the sort of=
 part where "quality" might be highly variable.)


This also showed up recently, via Adafruit:

> "In this video we explore the colorful science of fluorescence.
>=20
> "A really cool way to play with fluorescence at home is get a blue or vio=
let laser pointer and shine it into a dish or jar of water where you have a=
dded a drop of fluorescent highlighter fluid. You=92ll clearly see the beam=
 as the solution fluoresces in its path.
>=20
> "Now the common definition of fluorescent is something that glows a visib=
le color when exposed to ultraviolet light. Fluorescence is actually much b=
roader than that and you don=92t need ultraviolet light in particular. For =
example in the yellow fluorescent dye =93rubrene=94 both violet and green l=
asers will activate it and glow yellow. This proves you don=92t always need=
 ultraviolet light. But a red laser will not activate a yellow dye. Why is =
that?"


> http://youtu.be/CcssdJf0pKQ

BillW



--=20
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