Had a buddy give me one so I set up a fake blood trail one night. The only thing I could see is that it made the blood seem "wet" or "sparkle" a little. So I tried it on a dew soaked night, everything looked the same. If the blood is pouring out of a critter on a dry night, you will see it with the bloodlight, but then, who would need "help" in this scenario?! I gave mine back to my buddy!
I put it in the same category as the "kruncher" call, lol!