Re: Optical Brighters while using UV Filter
Re: Optical Brighters while using UV Filter
- Subject: Re: Optical Brighters while using UV Filter
- From: Graeme Gill <email@hidden>
- Date: Fri, 23 Jul 2004 14:57:20 +1000
- Organization: Color Technology Solutions
Roger Breton wrote:
Another area I'm having problem with is the source in these instrument. Yes,
the source is mostly tungsten -- Illuminant A. We all know that there isn't
much UV energy in Illuminant A sources to begin with.
There's not much UV energy, but the spectrum is very smooth, and
extends down to the UV. The ratio of UV to non-UV is significant,
and it is more than enough to excite an Optical Brighter (actual
Fluorescent Whitening Agent - FWA, since some OB's can be non-fluorescent
dyes) 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. This is easy to check using the Spectrolino.
Look at the spectrum of UV filtered, no filter (A), and D65 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.
Graeme Gill.
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