As for brighter lights, the only thing that will do is to blind the deer. They are primarily a nocturnal animal and over the centuries their eyes have adapted to "night vision". They see better at night than we do in the daytime. Bright lights blind and confuse them so if they react to the whistles at all they can't see where they're going. I don't ride or drive at night unless absolutely necessary but when I do my eyes are constantly panning back and forth. It's just a crapshoot.