"Radiant heat SON-T reaches deeper than convection heat LED"

Dutch grower Lans Zeeland has the first large greenhouse where tomatoes are cultivated under full LED. The ClimaLED3 system from QWestland provides white light and is equipped with a small fan that aids the lamp in reducing heat. In terms of design, the lights look more like SON-T luminaires than the red / blue bars used in most LED experiments. In the context of the monitoring project, which is financed by Kas als Energiebron (Greenhouse as Source of Energy), Wageningen University & Research, Business Unit Greenhouse Horticulture, follows this cultivation at Lans and additional measurements have been carried out into the temperature and light distribution in the greenhouse.

By means of a thermal imaging camera and ventilated temperature sensors, it turned out that the fan blowing down which reduces lamp heat would indeed result in a higher head temperature under the lamps. The smoke tests also showed that the air movement from the lamps does not extend beyond the head of the crop. This makes the temperature of the head under LED lighting higher than at the bottom of the crop. This difference is even higher than with SON-T and that is contrary to expectations. Apparently the radiant heat of SON-T lamps reaches deeper into the crop than the convection heat of the LED lamps. In itself this does not have to be a problem, but it is important to take this into account in the heating strategy.

Heat usage

Furthermore, the greenhouse with LED lamps has, in comparison with a nearby greenhouse with an almost equal consumption of electricity, realized a 1 °C higher greenhouse temperature and a 6% lower RH with 10% less heat usage. This is striking, because it is usually assumed that LED lighting actually leads to more heat consumption.

All lamps are suspended below the girder. This way they have to bridge a distance of 5 meters. And since the LED lights shine a bit more down than the wider-beam SON-T lighting, this gives a less even light distribution at head height (1.9 m below the light). Deeper in the crop the light distribution of the lamps is more or less the same. Whether the uneven light distribution is a disadvantage for production has not been established yet. Over time, all the crop heads will be straight under the light once. Moreover, it has been found that the temperature right below the lamps is ± 1 °C warmer than between the lamps. This can be an advantage when the crop gets more light.

This project is funded from the Kas als Energiebron program, the innovation and action program of LTO Glaskracht Nederland and the Ministry of Agriculture, Nature and Food Quality.

Read more about this project at this link. (In Dutch)

For more information:
Kas Als Energiebron
www.kasalsenergiebron.nl