The VA Division of Game and Inland Fisheries has studied this problem as Virginians suffer a lot of injury and damage annually (and in VA, automobile insurance companies do not cover animal collision damage**). They determined that plenty of light at night (high beams as oft you can use them) is your best defense. Deer are no more immobilized by bright light as moderate light, and it is better that you see them as far ahead as you can. Deer are most active and on the move, and willing to cross pavement, during the hours before sunrise and after sunset. Rutting season in November is particularly dicey. And "deer whistles" DO NOT WORK. It is a defensive driving matter.
** I was "fortunate" that we were in NH when I hit a 1500# bull moose with a 1200# Caterham! We were lucky with no injuries (the Seven had a homologated F.I.A. roll bar, somewhat like the smart's tridion); the Seven wasn't so lucky and went back to England for a re-build. The moose was less lucky still, and was put down by the Jackson police. It happened just after sunset in a mountain valley approaching Pinkham Notch.