Re: Optical Brighters while using UV Filter
Re: Optical Brighters while using UV Filter
- Subject: Re: Optical Brighters while using UV Filter
- From: Roger Breton <email@hidden>
- Date: Fri, 23 Jul 2004 08:36:01 -0400
Graeme Gill wrote:
>
There's not much UV energy, but the spectrum is very smooth, and
>
extends down to the UV.
I guess I never looked at Illuminant A spectral data below 400nm?
>
The ratio of UV to non-UV is significant,
What do you mean by 'significant'? Do you mean to say that all there is
below 400nm is mostly UV energy? This does go against my poorly held beliefs
that, in nature, only sources like daylight could contain significant levels
of UV energy.
>
and it is more than enough to excite an Optical Brighter
More than enough? Hmmh. How much is enough?
>
(actual
>
Fluorescent Whitening Agent - FWA, since some OB's can be non-fluorescent
>
dyes)
Is there such thing as Optical Brightners that don't fluoresce? Why bother
with those in the first place?
>
effect once the instrument illuminant intensity is divided out.
>
The FWA effect for illuminant A is perhaps half that for a D65 illuminant,
>
making it quite significant.
You mean 'significant' as opposed to expecting it not be there in the first
place?
>
This is easy to check using the Spectrolino.
>
Look at the spectrum of UV filtered, no filter (A), and D65 filter.
OK. I'll try that. But I'm curious how fitting the instrument with a 'D65'
filter can boost the UV input by two compared to the no filter?
>
A source that does have a low UV output is probably something like
>
a standard fluorescent lamp, since it is coated with phosphor that
>
has a high absorption at UV wavelengths.
And don't forget our friend, the sun. If I'm not mistaking, the sun's UV
output is mostly filtered (for now) by the earth's atmosphere. According to
the sun spectra I looked at on some web pages and in some books I have, I
tend to remember that by the time it reaches us that there is very little UV
energy left in its light?
>
Graeme Gill.
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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