Why would people be walking around a zoo at night watching Dinosaurs sleep though? I don't see what use there'd be for floodlights - if anything, in this setting, it would disturb the animals.
Frontier have claimed that they have captured the JP feel, I disagree when it comes to nighttime. If you think back to the movies, the main climactic events happen at night and therefore they should invest more time to creating a believable, JP nighttime.
Heres a short list of the cool things that happened at night:
T-rex break out
Nedry dies
T-rex chase scene
Brachiosaurus tree scene
Trex's attack the trailer
raptors in the long grass/compound scene
etc.
It needs to be treated well. Dinosaur breakouts aren't that scary during day time.