I have made this planet for my creatures and it is constantly dark, night or day.
No it's not a rogue planet, it's dark because of the 1,000 feet tall autotrophs that suck up all the sunlight and let little pass through (think nighttime with a half full moon).
There are also hot vents sticking up out of the ground and giving off a lot of heat which is absorbed by the bottom autotrophs (I won't go into the specific but heat makes the food for them) and the average temperature is 98 degrees Fahrenheit.
And this is a problem because of this: my creatures have superb vision, since they can see from microwaves to UV radiation on the electromagnetic radiation spectrum.
So my question is: what reasons justify a creature having such good vision on such a dark planet?