Mushrooms are not plants, so they do not require the type and amount of light
to grow like plants do.
Colonizing substrate should be kept in dark to make sure the substrate
doesn't pin prematurely.
Fully colonized substrate should be introduced to light to initiate pinning
- light "tells" the substrate that the conditions are right for forming fruit
bodies.(light is only one of the factors though, the others are lack of uncolonized substate, drop in temperature and lower CO2 levels.
Only a dim light is needed, anything too bright or warm will harm the cakes.
A fluorescent lamp or indirect sunlight is plenty of light. But basically any
kind of visible light will do.
A few hours of light per day is all that is needed, 10 hours is probably an
overkill. ( the book Mushroom
Cultivator states that 12-16 hours of light is recommended, but the experience
shows that much less is sufficient).
A source with a wide spectrum of light, especially containing lots of bluish
light (natural daylight or white fluorescent lights are very good examples of
light with lots of blue) is best, but a low wattage incandescent light (25 watts
is plenty) not too close to the terrarium will work well too. Also the use of
x-mass lights has been reported successful.