A tack on to that, rather than faffing around with lighting trying to find shiny spots, an easier way is with a guide coat. Mist on some cheap spray paint in a contrasting colour (any cheap and nasty spray paint will do). You are just misting it on, not going for a proper coat, so reactions with different finishes is unlikely. Some of the paint will settle in the low spots. You just sand till the colour is gone, then you know you have a levelled surface to work with. It's an old spray painters trick.