More Light or More Temperature? How RTR Answers the Question

“Does my crop need more light or more temperature?”

The answer is often: it depends. Growers can determine that using the Plant Empowerment Academy concept called RTR.

What the Radiation-Temperature Ratio actually connects

Light drives photosynthesis and sugar production, while temperature determines how quickly the plant uses those sugars. The Radiation-Temperature Ratio (RTR) connects these two factors and helps growers understand whether the crop is operating in balance.

How RTR steers the crop, in simplified terms

• High temperature relative to light can steer the crop more generatively
• High light relative to temperature can promote stronger vegetative growth
• A balanced RTR supports efficient energy use, consistent development, and crop quality

There is no single ideal RTR

The ideal RTR depends on the crop, variety, growth stage, climate, and cultivation strategy. However, once the objective is clear, RTR provides a practical way to evaluate whether light and temperature are aligned with the plant’s needs.

Calculating RTR from crop-level leaf temperature

Sigrow users can now use crop-level leaf temperature data from the Stomata Camera to calculate RTR and support more data-driven crop steering.

How are you using RTR in your cultivation strategy?

One acronym, two meanings. On this page, RTR means the Radiation-Temperature Ratio — the balance between light and temperature used for crop steering. The Stomata Camera also reports Real RTR, which stands for Real Transpiration Rate, a direct measurement of how much the crop is actually transpiring. Related, but not the same number.

For the longer explanation of how RTR works and how growers apply it day to day, read our full guide: Does Your Crop Need More Light or More Temperature? Understanding RTR.

Steering on RTR depends on knowing the crop’s own temperature, not just the air. The Stomata Camera measures leaf temperature, leaf-level VPD and stomatal behavior directly, while Air+ and Air Pro+ keep watch on humidity and CO₂.

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Want to discuss crop steering in your greenhouse? Reach out to the Sigrow team at success@sigrow.com (Mon to Fri, 9:00 to 18:00 CET) or support@sigrow.com (Mon to Fri, 9:00 to 21:00 CET).

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