求助：昼夜节律实验中的 Zeitgeber time 问题

请问这个long-day（18 1/6 days），和授时时间 ZT 0-18，哪些时间段是lights-on，哪些是lights-off呢。非常感谢

RNA was extracted from root, whole shoot, and shoot apex tissues from 8 week old, long-day (18 l/6 days) plants, harvested at ZT0, 6, 12 and 18