[Odd] Concrete looks darker under UV light...?

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patmurris
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[Odd] Concrete looks darker under UV light...?

Hi all!

I’ve had a Convoy UV S2+ (w ZWB2 UV pass filter) for a few years now and had quite some strange times exploring my kitchen and bathroom with it. I understand fluorescence and keep finding out what unexpected things a UV light can reveal… However, this is odd. Concrete seams between stones on my house actually become darker when i shine some UV light to them:

Warm white low ambient light – sorry for the blur:

Shinning the UV S2+ with ambient still on:

The pictures are taken with a pocket digital camera in auto mode, so exposure may have has varied, explaining the sharp contrast. But it looks the same in real life. The concrete seems darker with more light! It’s not just my vision adapting. The material goes from light gray to almost black, even with the ambient light still on.

Any thoughts?

EDIT: I think i figured it out, sorry for the trouble.

Looking at the upper left corner i can see the exposure has changed so much, even the stone goes almost black – hence the concrete seam looking much darker. However, the stone around the seam does fluoresce under UV light and produces the illusion of normal low ambient light. In contrast the seam looks darker. I just noticed other stones with mineral deposits that come out deep black under UV light. Concrete just does not fluoresce whereas this stone does a little. Is it?

Edited by: patmurris on 04/03/2018 - 19:56
wle
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the rock glows a little, the concrete doesn’t..?

wle

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patmurris
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wle wrote:
the rock glows a little, the concrete doesn’t..?

wle

Well, that’s my take on it…

kramer5150
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Isn’t it just differing levels of fluorescence in the rock minerals? Oh… be careful with your camera and UV light. Some CCD sensors can get damaged from UV exposure.

https://en.wikipedia.org/wiki/Fluorescence

alpg88
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it has more to do with visible portion of the light than uv, some colors do look different in blue light, i once turn on a blue light while bbqing, made me almost lose an appetite