Background

Delphy is a leading horticultural research centre in the Netherlands, running commercial-scale trials to optimise greenhouse crop production. In tomato cultivation, lighting strategy plays a crucial role in balancing yield, fruit quality, and energy cost. While dynamic light strategies offer flexibility in cultivation, their impact on photosynthesis and crop health in the greenhouse is not fully understood.

Previous studies have shown significant differences in the impact of consistent versus dynamic light conditions to regulate photosynthesis (Lawson, 2017). Fluctuations in LED intensity, such as those introduced by dynamic lighting, may reduce photosynthetic activation and cause up to 20% less carbon gain than expected. However, dynamic lighting can improve operational flexibility and reduce electricity use during peak times.

Introduction

In this trial, Delphy compared a fixed lighting regime with a dynamic strategy, aiming to evaluate differences in plant light efficiency, brix and yield across both winter and spring conditions.

The fixed lighting had typical LED lighting before sunrise, whereas the dynamic lighting dimmed the lights to maintenance respiration for three hours during peak electricity prices (6-9 am). Both compartments received the same total DLI by increasing the dynamic lighting intensity during non-dimmed periods. The key research question was whether short-term energy savings might come at the cost of long-term crop performance.

Gardin sensors were used to provide real-time, plant-level data throughout the experiment. By tracking photosynthetic efficiency, Gardin provided a continuous view of how the plants were responding to each light strategy. The Gardin Plant Indicators give insights into crop health, balance and productivity.

Results & Discussion

1. Fixed lighting improved photosynthetic efficiency at all light intensities

Gardin measured the photosynthetic efficiency (Fq'/Fm') of each treatment through Winter and Spring 2025. Light curves for each season and treatment show that plants receiving fixed lighting was more efficient at all light intensities (Fig. 1).

These measurements align with previous research by Lawson et al that more stable light exposure allows the plants to invest energy in optimal photosynthetic function. Specifically, greater development of electron transport proteins which significantly increased assimilation rates at saturating light and CO₂ (Vcmax, Jmax).

Figure 1. Light use efficiency (Fq'/Fm') over different light levels (umol/m2/s) in tomato plant. Left: December to February data, right: March to May data. Fixed lighting = red, dynamic lighting = green. Fixed lighting efficiency higher at all light levels.

Plant data collected by Delphy researchers showed fixed lighting plants were 5% more efficient at converting light into sugars, measured as the Brix / DLI (Fig. 2). This adds further evidence that fixed lighting allows the plant to put more energy into light conversion than dynamic lighting.

Figure 2. Left: Yield efficiency (kg/m2/mol) from December to April in dynamic (green) and fixed strategies. Right: BRIX / DLI (/mol) from December to April in dynamic (green) and fixed strategies. Fixed strategy generated 5% more brix per mol.

2. Real time detection of crop imbalance

In February, Gardin detected a 30% drop in crop balance in the fixed lighting crops which aligned with a 30% drop in yield in February (Fig.3). Before the imbalance, the fixed lighting had 8% higher yield and equal brix to the dynamic.

This imbalance, related to the plant's source-sink dynamics, may have redirected assimilates toward sugar concentration rather than fruit development, causing the yield drop. The dynamic lighting crop group experienced a smaller swing in balance and subsequently generated a higher fresh weight but lower brix in early March.

Figure 3. Left: Gardin's Plant balance. Middle: Delphy Tomato Yield. Right: Delphy Tomato Brix. Crop imbalance reduced fixed-strategy yield by 0.3 Kg/m2.

3. Photosynthesis impact clarified

Gardin data showed that the fixed lighting strategy resulted in 4% more photosynthesis (Fig.1), driven by higher light use efficiency at all light intensities. This is reflected in a higher plant health (Fv/Fm) for the fixed strategy, suggesting a stress response was triggered in the dynamic lighting, consistent with the hypothesis of reduced investment into electron transport proteins.

Despite similar final yields between the two groups, Gardin's findings support the hypothesis that the fixed lighting strategy produced more sugars and used light energy more efficiently.

Conclusion

This trial demonstrates the value of plant-driven data in refining crop strategies. Plant photosynthesis measurements contribute critical insights into short-term energy savings and long-term plant performance.

These results raise an interesting trade-off between the higher photosynthetic efficiency of fixed lighting and lower operational costs of dynamic lighting. The balance of 4% increased photosynthesis and a few hours of reduced LED costs will come down to the specific situation of a particular grower and growing season to determine the optimal strategy.

With Gardin, researchers gained real-time insight into crop health, balance and productivity. Gardin shed light on hidden stress and efficiency losses which impacted the tomato harvest. For commercial growers, this study shows how physiological feedback from the crop itself can guide smarter, more profitable lighting decisions in the future.

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References

Importance of Fluctuations in Light on Plant Photosynthetic Acclimation - S. Vialet-Chabrand, 2017