Literally the opposite of "in the dark" is "in the light":
I moved out of the darkness and into the light
However, it isn't natural to say "I'm in the light" in the same way we say "I'm in the dark".
Darkness is an absence of light. We tend more often to refer to the kind of light we are in, for example:
Don't run around in the dark - you should switch the light on.
It happened in broad daylight.
"Go into the light" is grammatically correct, it just isn't as natural. In fact, people are more likely to say "let's move out of the dark" than they are "let's move into the light". Also, "go towards the light" has idiomatically come to be a statement encouraging someone to give themselves over to death - not to take their own life, but to stop fighting an inevitable death. It is based on the idea that people close to death can see a tunnel of light.