"Pick up" is a phrasal verb and allows both variations. Turn the light on - The emphasis is on "the light". Turn what on? The light. Turn on the light - The emphasis is on "turn on". What should I do with the light? Turn it on.

Both variations are possible. The more syllables the object of a phrasal verb has, the less likely we are to separate the phrasal verb. Ex. We never say "Turn on it". That sounds very unnatural because "it" is only one syllable. We would always say "Turn it on". "Turn the big, red machine in the corner on" sounds a bit awkward because "turn" is so far from "on". This sounds better as "Turn on the big, red machine in the corner". If the object of the phrasal verb has too many syllables, the listener might lose track of the sentence and be surprised by the preposition at the end. In this case, it is better to keep the phrasal verb together (this is optional however). If the object has only one syllable, always separate the phrasal verb. Otherwise whichever option you choose is personal preference. I think most people would opt to separate the verb if the object is between 2-5 syllables, but it really doesn't matter as long as the object has more than one syllable.

There's no difference that I'm aware of. Both are commonly used.

The same both are correct