Basic chemistry to light up the phosophorus in the blood at the specific wavelength. The cheap way that works is a propane lantern. The burning of propane produces the right wavelength of light to really make the blood glow.

I tried the gerber light in the back yard with some spare blood I happened to have. Being color blind I am always looking for an edge. It worked well when the blood was fresh but with the dried blood i saw little difference from a regular flashlight. Nothing lights up fresh blood like a good old coleman. A coleman seems to make the blood glow.