Luminol
Luminol is a chemiluminescent chemical that is used in a variety of applications. When mixed with a suitable oxidizing agent, it produces a blue light. It is a white to yellowish solid, which is soluble in ionized organic solvents and does not dissolve in water. Because it reacts with iron, luminol is used to identify blood in crime scenes, and to biologists in cell analysis to detect copper, iron and cyanide. If you spray the luminol evenly on one area, the active oxidizer will illuminate the luminol. Light can be seen in the dark. The luminescence lasts for about 30 seconds, but the response can be recorded by taking a picture with a longer exposure. When sprayed, it should be evenly sprayed so that more amount is concentrated where there are many blood stains. The degree of luminescence is not proportional to the amount sprayed, but is proportional to the amount of traces left.