Do plants sleep under ultaviolent rays?
For this answer, I'm going to assume that by "sleep" you mean that it maintains a circadian rhythm/photoperiod. Recent unpublished research indicates that even protoplasts maintain their circadian rhythm under UV lights so the UV light isn't the problem. In order for the plant to "sleep" like you mention, the photoperiod needs to be maintained. The UV light needs to be on during the day and off at night. If you leave the UV light on all the time you would actually perturb the plant's photoperiod and it would be very unhealthy. Plant metabolism and photosynthesis requires both dark and light reactions. In summary...yes, the plant will sleep but you must maintatain the photoperiod by switching the UV light off and on.