--- In
Homebrew_PCBs@yahoogroups.com, Leon Heller <leon355@...> wrote:
>
> On 29/01/2010 02:50, James wrote:
> >
> > --- In Homebrew_PCBs@yahoogroups.com, James Bishop<bishopaj@> wrote:
> >
> >> It might also have something to do with the UV wavelength. I think
> >> LEDs have a longer wavelength, close to purple, while the tubes might
> >> be further into the UV range. This may affect exposure time or
> >> resolution.
> >>
> >>
> >>
> >
> > Fluorescent tubes emit light in sharp peaks of fairly specific wavelenghts. There are several peaks produced by the mercury vapor discharge itself, and others produced by the phosphor coating which is excited by absorbing the short wave UV from the discharge. Ordinary glass absorbs shortwave UV, so special germicidal and ozone producing tubes are made of quartz.
> >
>
> PCBs require long wave UV which isn't absorbed by ordinary glass.
>
> Leon
>
I never said they didn't. As I mentioned, there are multiple wavelengths emitted by the unfiltered blacklight UV tubes, the strongest being in the long wave UV range which is emitted by the phosphor being excited by short wave UV inside the tube. UV is by definition invisible to the human eye, what you see are various visible wavelengths also emitted by the tube. "UV" LEDs are not really UV, they are deep violet, but close enough that many UV sensitive materials respond to some extent.