• Far red light in tomato cultivation gives major differences between varieties.
• It can improve the sink strength and lead to a significant increase in harvest, but it can also negatively affect the quality of the green parts.
• At the moment, far red is not of interest for tomato growers. The production increase is disproportionate to the extra energy required.

Growers want to get as much as possible out of their LED lights. That’s why Signify is conducting ongoing research into the optimal application of Philips GreenPower LED lighting for various crops in close collaboration with its partners. Various light recipes are being tested in relation to energy consumption, light spectrum, additional yield, and uniformity. The use of far red has been one of the hot items in recent years and appears to have a positive effect on many crops when applied properly. Because of this, the question arises for many tomato growers who are already producing under full LED to investigate this?

At the moment, it’s not common to use  far-red light in tomato cultivation. Most commonly a fixed spectrum without far-red light is used. We do not expect this to change in the foreseeable future, but just want to be sure if it gives advantages especially in relation to the additional energy it consumes.. Nevertheless, we looked into cultivation effects we could achieve with different light spectra and also how we could steer different LED-wavelengths independenty from each other during the cultivation. So the question is would far-red light add something in a static or potentially dynamic light recipe?

In collaboration with Wageningen University & Research and vegetable breeder Nunhems, we observe unequivocal results when applying far red: we see that the available energy is easier to direct to the fruits. The degree of production increase when adding far-red light depends heavily on the variety. From other studies we see that the crop is slightly easier to control generatively, which sometimes makes it easier to achieve balance in the crop, and the crop may be slightly more forgiving in times when the growing conditions are not optimal. It is therefore too soon to say that far-red light in tomatoes has no effect at all on growth, quality or taste. But how does this translate into practice?

We also  executed a trial in Finland, one of the places on earth with the lowest levels of natural light where commercial tomato production in greenhouses takes place.  If we cannot proof far-red effects in Finland, our thought would be that it could not be proven anywhere else.. During the winter season we replaced 10% of the PAR-light for far-red light and tracked the crop-development and -production throughout the winter applying continuous far-red light. Although small visual differences, the conclusion at the end of the season was that far-red light had not been able to make a difference in production. We  even were of the impression that the crop under far-red light,was a little bit more susceptible to fungae diseases. Keep in min that if far-red light would have been applied for a shorter period of time other results could be expected.

For growers, the results have been mixed, to say the least. The research shows that there are major differences between varieties. Even when those varieties are genetically very closely related, there may be a huge difference in the effects. Now that breeders are developing new variety portfolios because of the resistance to ToBRFV, this has become an additional uncertain factor. There are also several results from our fundamental research that are difficult to translate into practice. For example, it turned out that different treatments with far-red light gave the plant better sink strength, which means that more sugars flow to the fruits. However, this only led to a significant increase in harvest if the far-red was dosed during the entire photoperiod -- in this case 16 hours a day. The production increase is therefore disproportionate to the extra energy costs required. In general, we see that the effects are greatest with large proportions of far-red. This sounds logical, but research also shows that the amount of far-red applied in practice in the cultivation of cucumbers and strawberries, for example, has a very limited effect. Recent field trials have also demonstrated this. When we apply 10% of the energy we use for lighting in the form of far-red light, we see the crop react to a limited extent. If we use the same amount of energy for PAR light, this yields equal production in a way that is currently less risky and at least as energy efficient. Other trials have given mixed results and only minor advantages, whether it was by using continuouse far-red light tretaments, or shorter parts of the daily photoperiod.

Some practical studies even showed negative effects from the use of far red. For example, the quality of the green parts can decline because the cells stretch more. This can be detrimental to the shelf life and potentially even affect the condition of the crop in the longer term. We even had to discontinue a number of studies earlier than planned to not let the leaf-volume decrease too much and keep the crop going. Next to this, we often observe a bigger negative effect at varieties which are known to be quite vegetative by nature.

In our philosophy, adding far red to the light spectrum only makes sense if it improves the business case of growers. Far red light requires more energy than PAR light, which leads to high additional energy costs on top of the higher initial investment. If we take this into account in our practice-based research, we draw a clear conclusion: at the moment, far-red light is not of interest to the tomato grower. We therefore continue to support our current light recipe for tomato cultivation. If you want healthier plants and more yield, go for MORE light and leave far-red light out of the equation. Of course, we will always keeps our finger on the pulse. If, for any reason, there is an impetus to take another look at the wisdom or lack thereof in using far-red light in tomato cultivation, we will not hesitate to take it up!