The 1/2 minus green filter proved to be too dimming for my liking. Growth seemed slow, just had a feeling it wasn't working out. So I replaced it with a 1/8 minus green, looks a lot better. First I was gonna use no filter but it really seemed too hot. Adding the filter brought it down to a better level.
Also, no bad effects from the 13.5 hour light cycle I started using a while ago. No reveging or getting loose or anything, just kept putting out new flowers while earliers one were browning, Blue Pyramid strain. Good amount of resin developing. I did just drop it down to 13 to aid ripening though, for the final week. I don't see any reason to go to 12 though. Why starve your plants? From what I've read on photoperiodism, there's no benefit in using fewer hours than the critical day length, which in Cannabis is apparently somewhere beyond 13.5 hours.
Well certain plants like Chrysanthemums will flower at their critical but to develop proper full size flowers it has to be about 10 hours, much shorter than critical. But that's a qualitative short day plant whereas Cannabis is an obligate short day plant, no separate flower initiation and flower development critical day lengths.