elk don't know the difference between head or clearance or backup or foglights. All they have to see is a light, whether it's direct or reflected off off of fog, trees, ice, whatever. If you can't get in in total darkness(or under red light), they'll start moving off.
There are exceptions to everything. A few years ago we were driving down a road in new snow just before total dark and spotted a herd of elk on a snowy hillside about 1/4 mile away. The only way to approach them in the morning was up that road. Before light the next morning, I drove up the road to near where they were, parked, and hiked the 1/4 mile to where we'd seen them, getting within easy range when it was barely getting light, just enough to walk without a light. They were still there, out in the open looking down on my pickup, and I shot a cow as soon as I had legal light. The difference here was that it was a well used road with some summer homes plus snowmobilers used it a lot. They were used to seeing cars both day and night.
