NECESSITY OF SUPPLEMENTAL LIGHTING FOR YEAR-ROUND PRODUCTION OF GREENHOUSE VEGETABLES

Good quality tomatoes and other greenhouse vegetables are in demand throughout the year. Contracts force growers in Northern areas to keep production going in winter, when light is limiting. A promising solution is the use of supplemental lighting. Since most greenhouse vegetable crops are very light demanding, rather high levels of lighting have to be applied. From literature reports it was deduced that for tomato production the daily light integral should not be lower than 12 mol m^-2 day^-1 (PPF). This implicates that at least during half of the year lighting is needed in The Netherlands.
This was tested on a commercial scale in the last two years, with 120 μmol m^-2 S^-1 PPF (10 kilolux). Production was continuous through intercropping. Production of tomatoes with lighting was at least as energy efficient as the unlit production.
The loss of light through shading by the luminaires can be reduced by a new luminaire, with only the reflector and lamp connector above the canopy, and the housing with ballast, starter and capacitor mounted lower within the crop.

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