Effect of Blacklight on Colors?

[marcchristopher]

Hi all,

I am currently trying to achieve a look similar to what is commonly called "black light effect". (And, yes, I agree, ideally this should have been done during the shooting. Unfortunately, however, for some reason this didn't work out and it's now my job to achieve this in post-production.)

So, I'm trying to understand what black light does to the colors of an image and I'm having a hard time to understand one pecularity:

As I have understood it, when most people refer to black light, they really mean "black light blue" (BLB) lamps. According to Wikipedia, "the lamp has a dark purple filter material [and] has a dim purple glow when operating". Why, then, do most colors (especially whites) turn into a darkish blue under black light, instead of purple? And why does it seem, as if this exact hue (between blue and purple) depends on luminance? (See, e.g., http://66.147.244.206/~uafsunst/wp-c...2-1024x682.jpg)

Or is there something I am missing? Can anyone explain to me what exactly is happening here? Has anyone ever tried to achieve a realistic "black light effect" in Photoshop (that did not look cheesy and amateurish)?

Thanks in advance!

[Redraw]

Re: Effect of Blacklight on Colors?

This article might help you with the what is happening part.

http://science.howstuffworks.com/innovation/everyday-innovations/black-light.htm

The "how to" in PS I am at a loss as I never really thought about doing it before.

[0lBaldy]

Re: Effect of Blacklight on Colors?

Is there a picture you could share that you would like to achieve this effect on? want the bright colors also?

[marcchristopher]

Re: Effect of Blacklight on Colors?

Thank you both for your help.

Unfortunately, I cannot share the images that I am working on, as my client does not want the "before" versions to be published: Basically, the models are dressed in bright, bold colors and the backdrop is more or less black. As I see it, this should actually be a good starting point for the look we would like to achieve.

Also, thank you for the interesting link. Indeed, the explanations are pretty interesting. As I have understood it, "black light" actually doesn't have a color at all. When something glows under a light black this is due to the fact that many "modern detergents contain phosphors that convert UV light into white light".

But why, then, do many objects seem to glow in different colors (blue, cyan, purple), depending on how much light they receive?

[skoobey]

Re: Effect of Blacklight on Colors?

Ah! The forum did something and my post went away. Anything with high density of right minerals glows under UV light.

Anyway, you mask out the lips, eyes, hair, everything but the skin itself, then you make skin black using a gradient map, refine it with curves to add that blue/pruple tint. Now, you want to apply some of the effect on the eyes, and teeth. You also might want to add extra purple to the eyes using a curve.

It's about black/purple skin and background being contrasted by bright colors that reflect.