God rays are those streaks of light that you get when there are small gaps in thick cloud cover. They stream down as if from Heaven itself. Rays is a plug-in dedicated to replicating this effect. It’s mainly for landscape images, but it can be used wherever you want a volumetric lighting effect.
It’s easy to set the ray’s length and brightness, and settings can be modified with sliders. Of course, it isn’t 3D so it isn’t really volumetric, but it does a good imitation of it by only streaking where there are light areas of the source image in the target area. This makes it ideal for skies where one bright area is surrounded by darker ones.
Very effective at what it does, but fairly limited in scope
However, as the light isn’t actually 3D, the streaks just run straight off. They don’t bounce, reflect or interact with anything. For that reason, it works best when looking in a skyward direction, with nothing in the immediate foreground that will give away the fact that this is purely 2D.