One of the mistakes that we as owners make (ok, its just me!) is thinking guinea pigs are a lot like us. In some ways they are in the way that they behave but in other ways, they very much have their own characteristics.
When it comes to whether guinea pigs like the dark or not, they are quite different to us. Guinea pigs are quite comfortable living in the dark and have eyes that adjust very easily to dark spaces. They can move around quite freely and are not inhibited by the fact that it is a dark space.
This is because as prey animals, they need the ability to move around tunnels and holes easily and at pace, so they do not struggle with dark spaces at all.
In fact I would say that they prefer darker shaded places more than places of sunlight. In the summer when it was very hot, they did not like being out in he sunlight and would always look to retreat to the shady areas.
I have also experimented with them being in darkened rooms and they are still happy playing Chasing around.
So if you are wondering for example whether you need to leave a light on for your guinea pigs, the answer is no you don’t have to. They are quite happy with the dark and can see better than we can in it.