|Authors: ||E.S. Runkle, S.R. Padhye, M.G. Blanchard, Wook Oh|
|Keywords: ||daily light integral, floriculture, long day, photoperiod, supplemental lighting|
Ornamental crops are commercially produced year-round in greenhouses throughout the world.
To reduce production time and increase plant quality, artificial lighting is used on numerous species to increase photosynthesis, create an inductive photoperiod, or both.
Lighting systems can be expensive to install and operate and thus, greenhouse growers seek effective and energy-efficient lighting strategies.
Supplemental (assimilation) lighting is generally most cost-effective when provided during a naturally low ambient photosynthetic daily light integral (DLI) and when crops are grown at a high density, such as in the production of propagative materials.
Recent lighting research with bedding plant seedlings indicates that the benefits of supplemental lighting are greatest when plants have developed a canopy of leaves to harvest the additional light.
Similarly, when the ambient DLI is low, increasing the DLI can reduce the time required for propagated stem cuttings to develop roots.
To accelerate flowering of long-day ornamentals, numerous lighting strategies can be used to truncate the night length.
Incandescent lamps are commonly used to create a long day, but they are electrically inefficient at producing light, have a low red-to-far-red ratio (R:FR) that promotes stem extension, and will not be available in many countries within the decade.
Compact fluorescent and rotating high-pressure sodium lamps are more energy efficient and have a higher R:FR, but flowering of some long-day crops is delayed relative to that under incandescent lamps.
Light-emitting diodes (LEDs) have the potential to be used for greenhouse photoperiodic and supplemental lighting, but research on ornamental crops is limited and presently, their commercial use is restricted to very specialized plant production situations because of their expense.
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