Re: Fluorescence
Re: Fluorescence
- Subject: Re: Fluorescence
- From: Juris Valdmanis <email@hidden>
- Date: Tue, 20 Feb 2001 21:26:21 +0200
hello everybody!
I'm get confused with all of this fluorescence stuff! May be you can help me
to get right with this?
I can't determine if my proofing paper counatins these fluorescent
brighteners or not!
From letter below I understood that, if UVfilter is used while measuring
paper, result should be the same for papers conntaining fluorescent
brighteners and for papers without them. Is it corect?
I also did some measurings with my paper. Measuring IT8.7/3 target without
UVfilter I get profile where neutral gray (15% K) stays neutral (16C 13M 13Y
0K), but measuring with UVfilter, neutral gray (15% K) becomes a little
bluish (16C 14M 8Y 0K). So this is what I can't understand, because I
thought that result should be the same!
Do you have any suggestions?
thanks,
Juris Valdmanis
Jelgavas Printing House
Latvia
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From: Robin Myers <email@hidden>
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Organization: Robin Myers Imaging
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Reply-To: email@hidden
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Date: Thu, 15 Feb 2001 21:47:50 -0800
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To: ColorSync Users <email@hidden>
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Subject: Fluorescence
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I would like to clear up a misconception that some people have about
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fluorescence. It is not only caused by ultraviolet radiation. Fluorescence can
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also be initiated by light in the visible spectrum.
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For papers and fabrics, fluorescent brighteners are part of the method used to
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make them look white. As part of their manufacturing process, the substrate
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materials are bleached to make them white, or as white as possible (the
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natural
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color for most papers and fabrics is yellowish), then they are treated with a
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fluorescent brightener to counteract any residual yellowness. In the case of
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fabrics, as they are laundered during their lifetime, they tend to return to
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their natural yellowness, so whites are rebleached and the fluorescent
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brighteners reapplied to maintain their whiteness. For a long time these
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fluorescent materials were known as "bluing" agents.
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Many white papers encountered in color management contain fluorescent
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brighteners that convert invisible ultraviolet light into visible blue light.
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This is an absorption of higher energy light and a re-emission of light at a
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lower energy. Since this is a process of higher energy light being converted
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to lower energy light, it can occur with higher energy visible light being
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converted to lower energy wavelengths of visible light. If anyone is
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interested, I can email them a graph showing an orange color measured with a
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GretagMacbeth Spectrolino both with and without a UV blocking filter applied.
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The results clearly show that the material continues to fluoresce when the UV
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light is completely blocked, thus proving that the fluorescence is caused by
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visible light.
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This means that the ultraviolet blocking filters will only effect the
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materials that fluoresce with ultraviolet light. It also means that any
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spectrophotometer can cause a fluorescence during its measurement if the
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material being measured will fluoresce with visible light, including the CM2s.
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So, why worry about visible fluorescence? Just put on an ultraviolet blocking
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filter and measure away. At one point in time, one very popular printer
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manufacturer produced almost all their magenta colorants as a fluorescent
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version. It made color matching almost impossible. Most manufacturers do not
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use fluorescent colorants, but you should be ever vigilant. Never assume your
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instrument will not cause fluorescence or that you are not measuring
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fluorescent colorants until you run a test. And if you are measuring paper
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with a fluorescent brightener, you should use an ultraviolet blocking filter
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for your measurements.
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Robin Myers
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