Contrasts: At dawn and dusk, open terrain may offer enough light to see deer clearly, but wooded areas may remain murky. Given time, your eyes will acclimate to the gloom. However, problems arise when you constantly shift your gaze from light to dark areas. Your eyes may need 15 seconds to adjust to highly contrasting light conditions. In that time, many a whitetail has made his escape. So, it's better to concentrate your hunting vision on one light condition or the other.