Wageningen UR Greenhouse Horticulture started a research project on assimilation lighting in horticulture with a low input of electricity. Tomato plants were planted on 23 October. Results of the season 2012/2013 showed that is possible to grow tomatoes with only LED lighting. Aim of the new project is to apply this knowledge in an energy friendly cultivation concept for lighted tomatoes. The research project 'More efficient use of electricity in lighted tomatoes' is funded by the Dutch Commodity Board for Horticulture and the Ministry of Economic Affairs.
Comparison hybrid lighting with LEDs
During last season, SON-T light was compared with hybrid lighting with LEDs above and within the tomato canopy. The lack of convective heat of the LED lamps was compensated for by maintaining a 1 °C higher temperature, which resulted in comparable developmental rates of the crops in the compartments with SON-T and LEDs. By adapting the lighting strategy early to the fruit load of the plant, the efficiency of lighting can be increased.
Energy efficiency of lighting
The question is currently how this knowledge can be used to increase the energy efficiency of lighting. Starting points of the experiment are:
- Make use of the natural light as much as possible by growing under a diffuse greenhouse cover with a high light transmission
- As much moles of light as possible from a kWh electricity in the greenhouse. A new type of LED of Philips is applied with an efficiency of 2.3 µmol/J
- As much light interception by the canopy as possible. This is controlled by inter lighting and a diffuse cover, and by measures to create a good crop architecture
- As much assimilate production per intercepted mole of light. We will use a light planning and continuous crop monitoring in order to avoid lighting when this is not necessary for the crop
- As much assimilates as possible to the harvestable product: find the right balance between production and use of assimilates. Production of additional stems and truss pruning based on the light demand of the crop.
Clear glass and diffuse glass
In the lighting experiment, we make use of two greenhouse compartments at Wageningen UR Greenhouse Horticulture. In the reference compartment with clear glass SON-T lamps of 105 µmol m-2 s-1 and LED inter lighting of 105 µmol m-2 s-1 were used with a maximum of 16 h per day. In the electricity efficient compartment with diffuse glass, we light with very efficient LEDs above the canopy (105 µmol m-2 s-1) and 105 µmol m-2 s-1 LED interlighting according to a light plan based on the crop demand. We intend to realize comparable production levels in both treatments, but with a 35% difference in electricity use.
Research questions in this experiment focus primarily on understanding what happens in the canopy under LED lighting. What are the differences in crop development and assimilate partitioning, and what are the underlying mechanisms? What is the gradient in photosynthesis from top to lower part of the canopy, especially when using inter lighting? How is the fruit quality determined by the lighting systems?
In the next months we will be able to answer these questions.