You would use 'like' in this instance. 'As' is usually used (but not always) when there is another 'as' in the sentence. For example: It was as bright as the night sky. If you wanted to use 'like' in the above sentence, you would have to remove the 'as': It was bright like the night sky. This is only an example of its use under one circumstance. It is a tricky grammar concept! Also, if this helps, 'like' is a preposition whereas 'as' is a conjunction.

It is best to use like here.