[jheriko]

that might work for a frustum like directional light source (maybe) but what about an omnidirectional point light like in the example?

you can certainly walk 'outwards' from a node but then you are missing the real benefit to the bsp for this problem imo... which is that you just carved the world into convex volumes.

convex polygons are easier to work with. they allow applying many more algorithms and make others trivial enough to re-invent on the fly as needed... instead of walking a structure at all you could keep a list of which edges are visible at each leaf node - if you have 'loads' of memory (e.g. > 1MB) then you might be able to store the edges themselves rather than indexes and mitigate memory lookup expenses as well (which are so far away from anything in a broswer... but yeah).