;; wrote:
nothing to add other than I notice the same thing. The darkness either makes me more cautious or raises my perceived exertion...there's just something about seeing far down the road that makes me run faster. I have done it a fair amount, and I've never been able to run comparable times to daylight unless it's cold and I'm trying to stay warm.
Conversely, running in darkness always had the opposite effect on me: I was able to run faster, with less perceived exertion, precisely because I couldn't see as far down the road as during daylight hours. It was like I was floating through space with the planet rotating beneath my feet. In his book The Four-Minute Mile, Roger Bannister described a similar sensation when he would train at night by running laps around a cricket pitch.