A light with a brightness of 1 has certainly no effect. Besides, your level is so bright you won't see much effect by lights anyway. And for a castle I'd use level geometry and not a model.

A piece of advice: Often people post their beginner's problems to the bug forum and then are surprised when the posts are moved straight to a beginner's forum by a moderator. Of course, bugs are always possible. But a bug would affect all users, not only you. When you see that the other users can create beautifully lighted levels, ask yourself what might be the reason that you can't. I won't know because I have no info about your level aside from the screenshot, but you have all information and should be able to ask other users the right questions.

Above all, read the Game Design tutorial. It's several years old, but the basics of doing a simple level including lighting haven't changed.