@riking Yeah, typo on my part there, sorry.  For dirt->stone, I meant that neither block emits light, and both blocks block light in the same way.  Therefore, no relighting calculation is necessary if one turns to the other, which was my original point.  For stone->glass, recalculation would be needed, because light-blocking has changed, and similarly for glass->water (although both transmit light, they transmit a different proportion of it).