I'm pretty familiar with my hunting areas and dont like how a flashlight closes out all outer vision and sense of direction outside the beam of light. I do however keep a small maglight in my hand and push the button on and off ever ten steps or so in case other hunters are in the area , they know I'm not a critter.
As far as deer being bothered, I've never seen a deer react badly to light. I've shined light on their eyes many times as I stood still and they hang around. But as soon as my movement ,smell, sound hits them, see ya!