"Is it bright outside?"
に is more of a directional particle than an adjectival one. So if you're going somewhere, use に. If you're already somewhere and you're doing something, use で. In situations like this where you're addressing a new specific topic, use は. When you're identifying something that was already mentioned in that conversation, use が.
Hope that helped some.
Just to clarify, が is something of a topic marker that highlights something in its sentence. According to my native Japanese teacher, it's also required in certain constructions like with 好き (すき). My impression from class is that you use は when marking a subject already identified in the conversation but が when you are highlighting a new topic.