I haven't used it in complete darkness, but at dusk, when cars had their headlights on and street lights were on, it recorded well enough for me to get the reg number of a bus that did a couple of close passes.
It does not like headlights lights shining straight at it... but who does?
@Grubbythumb how is the sj4000 in the dark? I'm thinking of getting one but worry it will be awful like a past cheapo attempt