Flaw in the movie

I'm talking about "Harry Potter and the Prizoner of Azkaban"

Of course there are a lot of flaws, I hear you scream. But this one is so blatant, and yet gets missed. And it happens at the absolute beginning of the movie. Know what I am talking about?

As the movie starts, you see a window glow with the light from Harry's wand as he tries to read his book under the sheet. And he hides by pretending to sleep everytime his uncle comes into the room.

Here's the problem. How is he saying "Lumos Maxime" and his wand showing the light? Isn't that magic? And aren't underage wizards forbidden to do magic outside of school?

And there in lies the flaw.

And it's a stupid flaw. There is no reason why the movies cannot stay true to the story. But no, they have to distort it for something more dramatic, despite the fact that the story by J.K. Rowling is already very dramatic.

But at least this part of the Harry Potter movies is better than the one that comes later. That one distorts the story to no end.

I am not sure how Rowling allowed it to happen.