Why White LEDs May be a Cost-Effective Lighting Option

By Greenhouse Grower staff|September 24, 2022

Researchers transplanted seedlings into 4-inch pots filled with peat-perlite media and grew them in a greenhouse under nine lighting treatments. Photo credit: Qingwu Meng, University of Delaware/American Floral Endowment

Many greenhouse floriculture crops are long-day plants, which means they require long days and short nights (usually less than eight to 10 hours of darkness) to produce flowers early. In areas where winters have short days and long nights, the flowering of long-day plants grown during that time is delayed or inhibited. To shorten long nights and promote flowering of long-day plants, growers can use dim photoperiodic lighting at the end of the day (day-extension lighting) or in the middle of the night (night-break or night-interruption lighting).

In the past decade, flowering LED lamps with custom light spectra including red (R) + far-red (FR) light have been commercially available for flowering applications. A more affordable option may be white LED lamps, which are mass-produced for general use. Developed for human vision, white LED lamps emit mostly visible red, green, and blue light, but little FR light. There are pros and cons to both, in addition to cost considerations. Flowering LED lamps with FR light can result in rapid flowering of some crops like petunia, but may also cause undesired stretching. White LED lamps may be less effective at promoting flowering than LED lamps with FR light, but may produce plants that are more compact.

In a recent research project supported by American Floral Endowment (AFE), Qingwu (William) Meng in the Department of Plant and Soil Sciences at the University of Delaware conducted an experiment on four long-day plants: coreopsis ‘Early Sunrise’; snapdragon ‘Liberty Classic Yellow’; petunia ‘Easy Wave Burgundy Star’; and petunia ‘Wave Purple Improved’. Results of the study, and key takeaways, are covered in a recent post on AFE’s website.