With high energy prices here to stay, we’ve seen big changes in the way growers are thinking about their use of light. High Pressure Sodium (HPS) lamps are being switched off and replaced with LED lights, which are not only more economical but have the option to be dimmed. Growers are learning that they still need to use artificial light, but it must be used smarter to combat costs - preferably without limiting crop growth, yield, or quality.

Two concepts are central to the new approach to artificial lighting: cost-effectiveness and flexibility. Plants need Photosynthetic Active Radiation (PAR) to grow. The trick to cost-effective growth is to give plants enough PAR light in the right composition of spectrum and intensity at the lowest possible cost to perform well. And just as electricity costs are not constant but can vary from hour to hour, a plant’s light requirements are not constant either. Research and practice have already shown that it can be beneficial for both plant development and energy bills to treat light as a dynamic growth factor. The days when light installations always ran at full power at fixed times will soon be a thing of the past.

What can growers do now to save costs without a dynamic spectrum, but with a continuously dimmable LED installation, a handful of sensors, and a modern control system? First of all, say goodbye to fixed patterns. Let yourself be guided by the crop and the daylight that’s already available, and supplement that as needed. Keep in mind that light correction is also an option in addition to temperature correction. You can therefore light a little more at the less expensive times in a 24-hour period (night and early morning instead of late afternoon and evening) and even change throughout the week (more on weekends, less during the week).

In a comparison test at Botany, we apply the principles of timing and light correction to tomatoes. The research is done in two compartments that receive the same light sum on a weekly basis. In compartment 1, lighting is kept at a constant light sum of 220 μmol/m2/sec. The lighting duration is adjusted to the expected solar radiation. In the adjacent compartment, dynamic lighting is provided at a maximum light sum of 300 μmol/m2/sec, but dimming is also used. It is controlled based on electricity rates. The lowest energy price is on weekends and at night, therefore providing the most significant light input. Measurements are also taken to monitor crop responses and plant processes, such as evaporation, photosynthetic activity, increase in biomass, physical yield, and fruit quality.

It is still too soon to make any definitive statements. Nevertheless, we already see increased favor for dynamic lighting. The energy costs are significantly lower, while the crop has performed similarly. We will undoubtedly come back to this later. How far do you think you can dim without sacrificing the quality?