Exposing light from day one, one jar out of a hundred will make an early pin or two, but I simply spawn those pins right into bulk substrate along with the grains with zero ill effects.
Stamets believes it's the hormones or other chemical triggers in the pins that do this. There is evidence they actually help to give a faster, more uniform pinset in the eventual flushes. Contrary to popular belief, a few pins in the grains can be spawned right into the manure or straw (or used in grain to grain transfers) and they do not rot or otherwise cause contamination. If a few pins form in the grains, it is actually a good thing. I've found no benefit or harm from allowing the grain jars to be exposed to light from day one. If you give light from day one, your yields will go up, and you won't face overlay problems. There is no reason at all to ever have your mycelia in the dark. Expose them to normal room lighting from day one. There is no harm or benefit from keeping jars in the dark. Those words were written by Stamets in TMC 20 years ago, and he disavows that advice today. The old advice of "incubate in total darkness" is bunk. LIGHTING COLONIZATION - Incubating dark is another thing in Paul Stamets 'The Mushroom Cultivator' that needs to go away. THEY'RE SOME MISINFORMATION/OUTDATED INFO SO CHOOSE IT WISELY. LC/AGAR/CLONING/STERILE PROCEDURE/HELP/PROBLEMS/OTHER CASING/FC/CO2/HUMIDITY/CAKES/OUTDOOR/SOAKING/MISTING