Science Into Practice - Crop lighting for ornamentals

The phasing-out of tungsten bulbs led HDC to investigate alternatives (PC 296).

Compact fluorescent bulbs are cheap but their spectrum lacks far red light, which impacts flowering and plant growth. LEDs can supply light at specific wavelengths.

Compact fluorescent bulbs were studied for night break and day-extension treatments for long-day and short-day ornamentals. Then two off-the-shelf LED systems were tested with modules to deliver red, far-red or blue light, or mixtures of red and far-red, and Philips' Green Power lamp in far red only, red and white and a mix of red, far red and white.

The fluorescent bulbs controlled flowering in chrysanthemum, poinsettia and fuchsia as effectively as tungsten but did not control flowering for half of the plants tested, probably because of the lack of far red, important for day-extension lighting. The Green Power lamps emitting red, far red and white elicited an equivalent response to tungsten in all plants bar Christmas cactus.

The far red lamps gave good flowering control for half the species but increased stretching. The red and white lamps were not useful except for chrysanthemum but proved better than tungsten with this species.

With the LED modules, red and far red combinations got a better plant response than red or far red alone. Effective flowering control of most species could be controlled by a mixed module of 25 per cent red and 75 per cent far red. But the high far red increased stretching in many species and using a 75:25 mix would be an improvement in most cases.

Horticultural Development Company

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