LED or HPS in ornamentals? A case study in roses and campanulas

The aim of the experiment was to evaluate the effect of novel top-installed high-output light-emitting diodes (LEDs) on ornamental plant production both in terms of productivity and energy use in comparison with conventional HPS lamps in two standard greenhouse compartments. The experiments were performed in late winter period using three varieties of potted miniature roses (Rosa hybrida) and two cultivars of Campanula grown in identical installed supplemental light levels (75–85 µmol m-2 s-1 of PPFD) with temperature set points 18°C at night, 24°C during the day, while 800 ppm of CO2 was supplied. Due to the winter being relatively cold, the set points were equal to the realized temperature as ventilation rarely occurred. The leaf temperature was maintained at the same level by adjusting the top pipe temperature. Two harvests were performed in February and in March to show the potential effect of winter-or early spring-grown plants. The results showed relatively small differences with respect to plant performance between the HPS and LED treatments, and most significant differences were found only in the 1st batch of roses harvested in February regarding plant height and stem fresh and dry weight, indicating that growth was favored under HPS lamps for three out of four cultivars. Both the 2nd batches for roses and campanulas harvested in March showed very limited or no differences between treatments. The energy saving on the electricity side was 60% in LEDs compared to HPS, but due to the increased heat use from top pipes the energy used for heating increased by around 50% over the whole experimental period.