Adding far-red light compensates for less light
Far-red light is not part of the PAR range, and is therefore not labeled as grow light. However, when far-red is added to PAR light, it has a beneficial effect on photosynthesis. Extra far-red light affects the assimilate distribution, and more assimilates go to the fruits. The question is whether these positive effects also occur when far-red light is used not as addition, but as replacement of (part of) the existing lighting.
Test
In the trial at Vereijken nurseries at the Beek en Donk site, part of the existing red/blue LED lighting was replaced by far-red light. Normal lighting provides 180 μmol/m2/s SON-T and 60 μmol/m2/s red/blue LED. In two test sections, the lighting was adjusted to give 40 μmol/m2/s red/blue and 20 μmol/m2/s far-red LED light instead.
In this greenhouse the Campari variety is cultivated with a stem density of 3.7 st/m2, planted in week 30 of 2017. In week 38 the adjusted lighting was started, from midnight to 6pm. An increase in vertical growth was observed up to and including January. There was no change in yield, however, which means that the decrease in growth light is almost entirely compensated for by the addition of far-red light.
Taste
The taste of the harvested tomatoes is periodically compared to the taste model. This predicts the outcome of a consumer test based on an analysis. This data makes it possible to track the taste of the tomatoes throughout the season. The model includes sweetness (refraction) and texture. On the basis of this data, a single number expresses how the tomatoes taste on a scale of 0-100. The analysis shows that the tomatoes get a higher taste rating from the treatment with far-red light. This difference is mainly caused by higher refraction and increased "bite".
The test runs until the end of the lighting season. During the test, dry matter determinations are made on leaves and fruits to get an idea of the biomass distribution. To map the temperature distribution in the crop, a thermal imaging camera is used and temperature measurements are taken at different heights.
This test runs parallel to an illumination test with far-red light in LED spotlight as part of the Carbon LED project conducted at Wageningen University & Research in Bleiswijk.
This project was funded by the Kas als Energiebron program, the innovation and action program of LTO Glaskracht Nederland and the Ministry of Agriculture, Nature and Food Quality.
You can find additional results of the study here.
For more information:
Kas als Energiebron
www.kasalsenergiebron.nl