I'm being specific, I'm not talking about "rendering", I'm talking about the rendering equation, which is the mathematical formulation of light transport. I agree it's amazing the brain is able to interpret the light coming into my eyes into a perception of reality, but the startling thing about lucid dreams is that it is also apparently able to very convincingly simulate the external behavior of light itself properly as well, without external stimuli. (Which is currently an intractable problem computationally FYI.) For example, when I turn my head in a lucid dream under conscious control, reflections, texture, etc, behave what appear to be normal, in real time. This blows my mind.