Milky mushroom fruits in light. The 2011 manual says light should be given for the maximum duration through the whole cropping period, but it gives no lux figure and no photoperiod.
TNAU is the only Indian source read here that puts a number on it: 2500 to 3000 lux for button formation, with cased beds kept inside a blue polythene tent. That is bright, roughly a shaded verandah, far more than a dim store room.