There are a lot of advantages to using an incident light meter, and you can read about them here. But what if you don’t have an incident light meter? Or you are packing light and don’t want to take your incident light meter with you? There are several less expensive alternatives.
One excellent alternative is an ExpoDisc. You put one on the front of your camera lens, point it at the light source, and use it like an incident light meter. Details are here.