Re: Perspex or Glass for UV Cover?

From: Yukio (yano_at_shaw.ca)
Date: 09/26/04 

Date: Sun, 26 Sep 2004 04:50:06 GMT

real question; What are you using for a light source ? A Blacklight bulb
with a UV max at ~ 360 or a Germicidal bulb with a UV max ~ 254 nMeter
wavelength. Without a spectrophotometer, to verify bandpass, easiest trick
is to use some of your UV sensitive material and run some test strips with
and without glass and or perspex and see if it changes the exposure time.

After you gather that data, it doesn't really matter what the wavelength or
cover material is . It either works or it sort of doesn't.
BTW Perspex is a ARCHAIC trade name for a Polymethacrylate plastic now
usually called Acrylic and often replaced with Polycarbonate or Lexan and
sometimes with polyethylene terapthalate.or even Polystyrene. So just
because it clear and it is made of a rigid plastic and not glass does not
mean it will behave like Perspex.

Same story with "Glass!!, After all , both types of UV Lamps are made of
"GLASS". Most comercial glass is a Soda Lime Silica glass and will block
Short-Wave 254 nMeter UV. light. Germicidal UV lamps are constructed
with a High Silica or Quartz glass envelope. This is why an ordinary light
bulb is "Safe" from a UV hazard point of view, (soda-lime glass envelope)
but Quartz Halide bulbs must be operated with an appropriate UV Shield in
place. The high operating temperature makes the Quartz glass envelope
necessary but a soda-lime glass filter must now be ftted to block the
excessive amounts of UV being generated. Ordinary incadescent lamps are
cheaply manufactured using a soda-lime based glass which fortuitously blocks
any shortwave UV that is generated..

In summary you are going to have to run test strips anyway no matter what
you are told. So take everything with a grain of salt . NB. Some UV
Photo-sensitve materials materials react better to Longer Wavelength UV than
Short (254)nmetersUV.

Yukio YANO
VE5YS

  "John Dough" <1@2.3> wrote in message
news:59idnUxxlt0jNcjcRVn-ig@is.co.za...
> Hi all,
>
> I'm busy building a UV box for photosensative PCB's
>
> I've read various posts about how you shouldnt use glass to cover the
> artwork as it stop UV rays. I've also read a few post where they say don't
> use perspex - use glass!
>
> Which is it :)
>
> Is anyone using glass successfully? Or is perspex better? Or nethier - is
> there something else I should look at?
>
> Thanks
>
>

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