Cucumber crop size of great importance for light interception

The amount of crop appears to have a major influence on the loss of light upwards and downwards. This is shown by measurements of light interception from WUR Greenhouse Horticulture. The measurements were done in the autumn of 2017 on two farms with high-wire cucumber cultivation and a different orientation of the LED interlighting. The total loss of light to the greenhouse roof and greenhouse floor was 4% on one farm and 19% on the other.

Leaf quantity and crop height

This was largely due to clearly visible differences in leaf quantity and crop height at the time of measurement and possibly due to the orientation of the interlighting. At the cucumber company with a lot of light loss the crop was very open compared to the other company. In combination with the vertical lighting modules, which are illuminated over a larger crop length, light is reduced downwards and upwards depending on the position of the lamp. The amount of crop also affected the amount of PAR light that was measured in the middle of the walkway. At the two companies, that was 17% and 34% respectively. However, this light is not lost by the crop, because this light will be largely absorbed by the cucumber plants on the other side of the walkway.

The measured interception of the sunlight by the plants was 96 and 87% respectively on both farms. On the one hand, it is positive that a lot of light is collected. However, the lowest crop layer is therefore hardly lighted and may not be efficient.

Vertical interlighting

At the cucumber company with vertical interlighting, the production could be compared with the unexposed part in the greenhouse. 1% more PAR light from the interlighting led to 0.8% more production over the whole year. The higher stem density with exposure in the second crop will have positively influenced this. Due to further optimization, through, among other things, the stem density and an adapted fruit cutting strategy, it must be possible to further increase the light efficiency.