I do not like the new "smooth lighting" algorithm. I get a headache playing Minetest just due to eye strain it's causing. Frankly, I think the light mapping curve in 0.4.15 looks ridiculous. I see patches of roadway with ghost shadows in broad daylight. I see bridges where the entire superstructure is illuminated by a single torch. The entire scenery looks anything but realistic, just a messy patchwork of dark blobs and glowing spotlights at nighttime as well as in caves and mines.
Surely there has to be some way to disable this horrible new feature?
This is not due to official 'smooth lighting' or lighting bugs, it's the new light curve that makes light spread further from light sources, making light sources effectively brighter. We have reduced the light level of torches by 1 in MTGame to compensate and create a difference between torch (12), fire/lava (13) and meselamp/growlamp (14). Light nodes in mods may need to reduce their light levels to work better wth the new light curve.
The light curve can only be changed in engine code but maybe you could open an issue to make it configurable?