My reference to “classroom theory” is because in this torch the temperature sensor is not closely coupled to the parts that are trying to be controlled. So it is a lot more difficult to do, and I am impressed by how well it works.
I regard what TK is doing as a pragmatic approach, using empirical methods, rather than a theoretical analysis.
Control engineering is quite a deep subject, I only studied it just enough to realise how little I understood.
See e.g.
to get an idea of some of the complexity.
No idea about Zebralights, but clearly they are doing something right. ISTR from posts here that DrJones has developed some impressive temperature control as well, but can’t find the details.