Black lights in CSI-type shows

Blacklight BodypaintingWe've all seen it at least once. The CSI crew are at the scene of a crime, looking for evidence. They turn off the lights and awesome techno music starts to play. Out comes the gloves, goggles and black lights. They proceed to sweep the lights over the entire room until - There! - a telling blood splatter appears on the wall or bedsheets. The crime then becomes solved, thanks to the discovery. I've even seen them go so far as to find bodily-fluid stains on washed laundry, and showing through freshly-painted walls.

On a less dramatic note, there was once a blind dating/matchmaking show where one person got to pick out of three contestants which they would go on a date with, based on several criteria. One was that they got to snoop around their potential date's bedroom to try to deduce something about their personality. Part of this snooping included a black light test. None of the episodes I watched revealed anything interesting under the black lights, but many contestants got nervous at the prospect.

The last area I tend to see the use of black lights is in hyperbolic stories about dirty hotel rooms - taking a black light to hotel bedsheets reveal several disturbing stains in this segment, for example.

And its all made me wonder. Do all bodily fluids glow under UV lights? Can you wash these stains away? And what would the average person's bathroom or bedroom look like under UV lights?

First up, blood doesn't glow under black lights. It can be detected, but it doesn't glow like other bodily fluids:

Since body fluids like semen, saliva, and vaginal fluids are naturally fluorescent, the use of a light source offers a unique method for locating them. A crime scene investigator can narrow down the specific locations of stains for collection instead of testing entire, large pieces of evidence such as a mattress, a carpet, a sheet, an article of clothing, etc... The dried body fluids will actually glow under the light source illumination.
[...]
Although blood does not glow in the visible range, it has a unique color band (wavelength) under which the blood stain will darken to enhance its contrast by approximately 4 times. This is most effective in photographing blood prints because more of the detail of the blood print will be revealed by the enhanced contrast.

So they can still see blood stains (but they aren't bright, like I've seen some shows depict). Ladies, beware! You may be marked as a murderer as your toilet, bathtub and bedsheets might show traces of blood! All you poor folks who drool in your sleep might look like you've been up to no good when someone shines a UV light on your pillow. Anyone who owns a pet who has ever had "an accident" might be suspected of something nefarious... To be more accurate I think CSI should depict a realistic scenario where all beds and bathrooms they encounter are covered in bodily fluids - at least, according to that one episode, you can't wash the stains out completely.

Can you?

The answer is "yes, but..."
Some stains won't come out in a normal wash, depending on your detergent. Some will require something fairly powerful, like urine stains in a carpet. Things like semen and saliva should come out easily, but urine and blood can be rather stubborn, though I suspect a good bleaching would take care of them both.

Point is, the TV shows got it wrong again. Blood doesn't glow but it's visible. The average persons' bedsheets, for example, won't be innocently clean except for the single incriminating stain - unless they did laundry that morning, perhaps. And I can't imagine what they'd think of a raver who spilled a bit of black light paint.
We all look like murders under the glare of a UV light.

0 things about

Black lights in CSI-type shows

Post a Comment

Copyright 2012 Phile not Found. See About
Powered by Blogger

"Whenever you find that you are on the side of the majority, it is time to pause and reflect."