Im not trying to argue with anyone on this topic, but i had my lights run 24/0 for a month now and just now started a 20/0 period.. and from my experience the plant seems to pick up alot of growth in its short dark period.. i dont want to get technical with all of you its just something i noticed, more like a break than rest and whether its been tested time in an time out you just never know how each individual will react to a little darkness, mine seem to pick up growth with 4 hours of dark and kinda gets them ready for the next 20 hours of light..