[Xcelerate]

> It better handles more complex light effects like caustics.

I wouldn't say better. I would say it provides an approximation to the rendering equation more quickly than path tracing does. However, photon mapping is a biased algorithm, which means that if you average many independent renderings together, they won't converge on the correct (exact) image. Path tracing methods (bi-directional, Metropolis, etc.) converge on the exact solution, regardless of how noisy each individual rendering is. (However, it may be the case that an unwieldy number of samples is required for tricky caustics, so in practice, path tracing may fail to produce a correct result because of high variance.)

[tomvbussel]

Photon Mapping might be biased, but it's extremely easy to make it consistent by using the method outlined by Knaus and Zwicker [1]. Using that method photon mapping will converge to the right result. Even without progressive photon mapping you can choose a photon radius that won't cause visible errors.

[1] http://cgg.unibe.ch/publications/2011/progressive-photon-map...