forensic crime scene light

I’m looking for an effect similar to http://www.youtube.com/watch?v=MW2tZGatwSA at 0:40 (Condemned Criminal Origins) when the player pulls out an ultra-violet light and scans it over a body or object and bodily fluid or hand prints appear. How can I pull this off?

You can put the invisible objects on their own layer and have a light that culls all other layers or a camera that renders only objects on the invisible layer and then use a round render texture to display them over the main camera

how do you make a round render texture

isn’t there a shader out there that allows you to apply 2 two separate texture layers and then control the level of transparency based off the amount of light

http://forum.unity3d.com/threads/26639-Reveal-texture-only-when-light-falls-on-it - Solved