Assimilation light in greenhouse crops

In horticultural practice the distribution of assimilation light within the crop is one of the most discussed issues. Since costs for light, and thus energy, do not seem to stop increasing, an efficient use of assimilation light is of considerable importance for growers. Apart from the lamp positions, the lamp type and its emitted colour spectrum affects its energy consumption, e.g. LED lights are more energy-efficient since a negligible amount of energy is lost by heat dissipation.

The project:

Our 3D models are able to calculate distribution and spectral composition of the light within a crop stand. Such simulations may replace costly and time-consuming experiments on the fate of incoming light. Moreover, these models may provide an alternative method to costly experiments, to test different lamp positions, colours and crop structures in silico. These reasons have convinced the Dutch Horticultural Production Board (‘PT’ or Productschap Tuinbouw) to fund this research on 3D modelling of light distribution. The project has been carried out between March 2008 and beginning of 2010 by WUR-Greenhouse Horticulture in co-operation with the WU-chair Crop and Weed Ecology, Philips, Hortilux and some growers.

Some project details:

  • Examined crops were: tomato and rose
  • The modelling platform used is: GroIMP (see for background information).
  • Measurements: a representative crop-greenhouse combination for each of the two crops has been examined on (1) current 3D lamp positions and natural light conditions, (2) 3D structure of the crop at several growth stages, (3) light properties of greenhouse cover, lamps, greenhouse interior and plant organs, i.e. reflection, transmission and absorption at various wavelengths.
  • Modelling properties: Using an inversed ray-tracing method, the 3D model is able to simulate the local (i.e. per leaf) absorption, reflection and transmission of light of different wavelengths. Net assimilation rate as well as daily assimilation as a function of leaf area and absorbed light is computed for each organ of the virtual plant. Net production is estimated for different growth stages, at different light strategies. This enables us to evaluate the strategies for their impact on growth and associated light and energy use efficiency.
  • In an accompanying project photosynthesis at the various wavelengths has been examined, thereby quantifying the effect of the light spectrum on photosynthesis, and thus, growth.


P. de Visser & G. Buck-Sorlin (2011). Modelling spatial light distribution in crops (Modellering ruimtelijke lichtverdeling in gewassen). Report GTB-1104, Wageningen UR Greenhouse Horticulture