| Mayres, I don't know whether there is an actual minimum night required. I even remember a post, somewhere that totally escapes me at the moment, about someone who had his lights on for 24 hours a day for months at a time and did not report any adverse effects on his orchids. I've never tried this and don't think that I will (all that brightness at night + even higher energy bill = not for me).
The shortest "night" I've ever seen referenced anywhere for orchid culture under lights was 6 hours, with an 18-hour day, at the height of summer. What has been consistent across the web and book references I've read, though, is that there has to be some kind of gradual seasonal change - longer days in summer, shorter days in winter. |