I finally finished writing the next article about the lightmap rendering tech that I did for The Witness. This one is about irradiance caching, and in particular I describe how to estimate irradiance gradients when the irradiance is sampled using a hemicube distribution. I'm afraid the article is a bit too specialized and I suspect it will only be useful to those that are trying to solve this particular problem, but I think it's good to have this documented anyway. This time around we are trying something new and we are cross-posting it on #AltDevBlogADay. It seems to me that most of the subscribers to The Witness blog are non-programmers, so this way it may reach a wider audience. Hopefully this will also encourage me to post more regularly!