I took an out of state elk last year with a illuminock nocked arrow. The down fall with these is that with a fast FPS and slim carbon arrows if it goes clean through the animal the light will many times disengege. It only takes a small pull backwords for the contacts to break the connection (there designed that way). Every time I have used them wether deer or elk they are off when I retrieve the arrow. If the arrow doesnt penetrate and the nock and fletchings are outside the animal then you are good...so dont be surprised if you dont see the light at night.