What
is the ruling on making salah in the dark, where you can’t even see your
own hands?

Praise be to Allaah. 

If
the conditions of prayer are fulfilled and the essential parts or pillars
of the prayer are completed, then the prayer is valid. Light is not an
essential condition of prayer or an obligatory part of the prayer. But if
the darkness is a cause of fear which disturbs a person to the point that
he cannot have the necessary presence of mind and humility (khushoo’) in
prayer, then it is makrooh for him to pray in the dark.