Seedlings were grown under natural short-day photoperiods (12 hours or less) and night-interruption treatments were delivered from a rotating HPS lamp mounted at one gable end of the greenhouse or from incandescent lamps that were illuminated continuously for four hours or cyclically for 6 minutes every 30 minutes for 4 hours. Within 16 weeks, 80% or more of the plants of each species that received night-interruption lighting had a visible flower bud or inflorescence; all species but petunia remained vegetative under the short-day treatment. Flowering of all species grown at 13 meters from the rotating HPS lamp was delayed by 14 to 31 days compared with those under continuous incandescent illumination.
The researchers estimated that the weekly cost to operate night-interruption lighting was an impressive 80% to 83% less than the cost of continuous incandescent lighting. According to Blanchard and Runkle, "a rotating HPS lamp operated continuously during a 4-hour night-interruption was effective at promoting flowering in these long-day species and consumed less energy compared with incandescent lamps operated continuously." The researchers concluded that use of rotating high-pressure sodium lamps could be effective in commercial production as long as the light intensity is above the recommended value.
|Contact: Michael W. Neff|
American Society for Horticultural Science