Influenced by the energy market, the approach to lighting is changing. Focus on maximum production is being exchanged for the most efficient use of your available energy. The great thing about LEDs, which use about half the amount of energy, is that they bring this new lighting strategy within reach. This makes it possible to start thinking in ‘as much gram tomato/kWh as possible’, instead of ‘as much production and/or the highest light efficiency as possible’. A considerable difference, which also affects other aspects of cultivation.

The transition to LED lighting has gained momentum and this development still continues. But as a grower, you should be aware that when you tweak the lighting, this will also have consequences for the rest of your cultivation. Growing with LED influences the climate in the greenhouse, for instance. Because less HPS means less radiation heat, and so a different heat division and moisture balance in the greenhouse. To overcome that, you can choose to use the grow pipe as primary heating, over the pipe rail. The grow pipe has a more direct effect on the plant temperature and growth speed of the fruits, causing the shift in emphasis for many tomato companies.

Furthermore, LED lights have the advantage that they’re dimmable and don’t radiate heat. This separates heat from light and makes more lighting hours possible with LED during times of the year when the temperatures rise You are able to to quickly react to changes outside, but also to fluctuating energy prices. This means you can switch on- and off in stages. Next to that colors can be steered through the Philips GrowWise Control System to give the crop optimal light spectrum during the day or the growth cycle.

Growers will further align their lighting and climate strategy with LED. To fully benefit from the advantages, two energy screens combined with dehumidification systems are used more frequently. That is the only way to take full advantage of the light output and save a maximum amount of energy at the same time, without compromising on the greenhouse climate. There is more focus on dehumidification. In the meanwhile, you should keep an eye on the plant temperature and focus on crop development and production.

During this winter, growers have looked for the limits and have discovered which minimum temperatures and light sums are still acceptable. Some dropped below the bottom line and saw the crop growth and ripening slow down too much. The bandwidth differs for every crop, but in general you can say that with less than 90 Mol/m2/wk, combined with too low temperatures, growth will slow down considerably and both production and quality are affected. The crop needs a certain light sum to stay healthy, and moreover, asks a certain amount of light to maintain the given plant load at a certain moment.. The amount of energy should be just right for the plant load and stem density of the crop.

When weather conditions in winter are mild, like they have been often in recent years,  growing with mostly LED has gone well in most cases. However, should it be a cold winter, there is a risk that the crop will grow too vegetatively and strong during the first months of lit cultivation. A good and consistent crop buildup requires good coordination between the light sum and plant load. More light is not necessarily better in that case.

No grower wants a crop development that is too vegetative, because that means the fruits will remain too small and the crop grows too slow, leading to quality issues. It is advised to use growth- and photosynthesis models for a good buildup, giving you the possibility to monitor and steer the crop. Crop advisors or Signify’s plant specialists can offer support.

Besides the buildup of the light sums, the transition to natural light in spring should also happen ‘with caution’. For example in a very bright month early spring helps scaling down on lighting quickly and save money by doing so. But despite the good daily light sums, in retrospect it appears that the use of light has been inadequate in several cases. Research shows that the spring production of many tomato growers is less than expected. This teaches us that integrating a gradual transition in the balance between the sum of artificial light and natural light is key. As well, the hypothesis is that keeping a certain day length plays a key role as well.

Don’t forget to also keep an eye on the reduced evaporation as a side effect of full LED lighting. This causes a reduced water absorption and with that the uptake of fertilizers. You can anticipate this by steering for a higher EC-value.

It continues to be a matter of finding the balance. With fluctuating energy prices you will again have to look for the limits.. But you should remain cautious. Because when lowering the light intensity, there is a risk that during the winter months too little light will penetrate to the bottom parts of the plant. That is why it’s important to keep the structure of the crop open. That means you should pick enough leaves so that the lower leaves can also absorb enough light.