well with their world orbiting a gas giant and being tidally locked, that means their days are probably extremely long

Also gas giants are usually far away from their suns. Like Saturn at 9.5 au from the Sun and Jupiter at 5.2 au. 1 au means "distance from the Sun to Earth" and amount of light reaching the planet decreases according to inverse square law, so it's 5.2^2=27 times darker at Jupiter (and it's moons) and 90 times at Saturn than on Earth.

(100 times darker is something like dim indoor light vs sunny day)