In late on this topic, but thermals should not be used for any game hunting regardless of day or night. I have no problems with killing predators, but on big game it's a no go for me. Depending on your level of experience with thermals and more importantly the quality of the thermal unit, picking up targets out to 1500 yards is easy to do. Some units have auto scan, built in lrf, ballistic correction for yardage and incline, and many other features that makes it extremely unethical in my opinion.