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UV mysterious

laserdelic

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If you have watch the CSI serie, probably you have seen a orangish filter, that combined with a UV torch, make evidences fluorish. I thought it was a sci-fi license of the TV until watch this:








I must confess that Im kind of lost. What are they using to take this photos, only UV light? Some filter?. Would a unfocused 405nm laser be useful for getting something similar?
 

Cyparagon

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It's a common misconception that body fluids glow under UV light. They add a substance that binds with proteins to make it fluoresce. 405 doesn't work nearly as well as 370 (From a fluorescent black light for example) for fluorescence.

I don't see the point of making fingerprints glow though. Any black powder binds to the oil and makes it visible without the aid of a lamp. They then put tape over the powder to extract the pattern as far as I know. CSI is about entertainment, not reality.
 
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Besides, the orange filters would be for protection from the UV light while allowing the "evidence" flouresceing to be seen.
And from what I understand the reaction is short lived and can only be done once as a chemical process occurs that prevents it from being repeatable. They have to be ready for the result before attempting anything.

As far as using lasers to help with fingerprints... again from my understanding, they can use lasers and the precision of the wavelengths/bias of the reflected light to enhance and reveal details of multiple layers of prints on a single surface.
So if one set of prints is on top of another they can sometimes use lasers to "seperate" the two for accurate imaging and the resultant database searching.
 

laserdelic

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Well, looking at some forensic sites, like the one of the upper photos, you can see that some of the CSI´s parafernalia is at least partialy true

http://www.advanced-ndt.co.uk/Forensic_Lighting/
What body fluids are fluorescent by nature?

• Semen (DNA)
• Vaginal secretion (DNA)
• Urine (DNA if it contains blood or other body fluid)
• Sweat (DNA)
• Saliva (DNA)

Semen

Semen is very fluorescent by nature and the fluorescence can be observed on dark as well as light textiles when illuminated with an intense UV light, without the need for using coloured goggles.

Vaginal secretion

Vaginal fluid is very hard to detect at all times, as it has a very weak fluorescence.
In fact I think they have cheated that photos. Probably they just have dip the finger in some fluor powder and left the fingerprint right in the place to take the photo with a good UV illumination
 
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Actually, the CSI TV show does employ some notable scientists from the fields they deal with in the programs.
It is just that the scientific accuracy is usually "modified" for the viewing audience whether because it is too complicated or because divulging some details can lead to explotation of the information by certain individuals. (No helping the criminals needed.)

That fingerprint looks like it was dusted with a flouresceing powder. Nothing too fancy or hard about that.

As far as other "fluids" flourescing I will say that for all the years that I was renting places to live I always did some extremely revealing walk-throughs with the owners around dusk when considering a place to live.
They always had the same puzzled look when I would show up with my 18" black light and an extension cord.
After the walk-through they would know a lot more about stains and such AND they didn't like what my black light cost them !
:D
So many dishonest people claiming "new" carpets and "never had pets" etc.
Turn on the light and see all the bright marks, then there are the oily smears on walls, don't think about bedroom floors, and only the strong of stomache should consider how a few bathrooms have glowed but only one had a surprise on the ceiling.
(Now all that I left had a surprise left on the bedroom ceilings of a much nicer nature. I would create a starry night using small bits of glow-in-the-dark tape including a few notable constelations with random spots filling in. After the black light was on for a minute you could lie on the bed looking up and feel like you were outside on a clear summer night.)
:)
 




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