The added value of LED assimilation light in combination with high pressure sodium lamps in protected tomato crops in Belgium

The total area of protected tomato crops in Belgium comprises 450 ha. In 2014 only 11 ha were lighted crops. One year later, this number increased with 400% towards 55 ha. 53 ha are equipped with high pressure sodium lamps (HPS), while the remaining 2 ha combine these lamps with light emitting diode (LED) assimilation light strains in between the crop. High pressure sodium lamps are not energy efficient. A lot of energy is wasted as warmth in comparison to LED light. In order to explore the full potential of LED light in protected tomato crops in combination with high pressure sodium lamps, a trial was set up at Research Centre Hoogstraten, Belgium in October 2014. High pressure sodium lamps (SON-T, Philips) of 169 mol m(-2) s(-1) were installed in a tomato greenhouse compartment of 500 m(2). In four plant rows (total: 100 m(2)) a combination with LED assimilation light (two interlight modules of 55 mu mol m(-2) s(-1)) was made. These two LEDs were hung horizontally on top of each other at a distance of 70 cm. The height relative to the plant was adjustable according to the cropping stage. Two tomato cultivars were planted on the October 22, 2014, each at two different plant distances (3.33 and 4.17 stems m(-2)). A comparison in crop parameters and production was made for each cultivar at both plant distances grown under high pressure sodium lamps with or without additional LED assimilation light. Results are very promising for both cultivars with increased yields of 20% with HPS and LED light. For practice, more research is needed to optimize plant distances, light strategies and light intensities to make the technology more profitable and durable.