I think it depends on the plant - some are photoperiodic and rely on light/dark cycles to initiate blooming. On the otherhand I have had fluorescents on 24 hours a day for 4-5 years now and my paphiopedilums grow perfectly well. At 10:19 AM 1/7/98 -0800, you wrote: >Anyone know if there is any harm in 24-hr. flourescent lights on plants >(plants that don't get any natural light)? Or is there an optimum number of >hours/day for the lights to be on? > >Heather > > Anita Dille e-mail: adille@soils.umn.edu beancounter...and proud of it