Leaf & Canopy Temperature Sensors Explained for Plant Physiology Research
The LT-1T leaf temperature sensor, available from Implexx, is a high precision, scientific sensor for leaf temperature research.
Leaf temperature sensors measure the temperature of individual leaves so researchers and growers can understand transpiration, stomatal regulation, crop water stress, and irrigation response. When paired with nearby air temperature, leaf temperature data can be converted into leaf-to-air temperature difference, a practical plant-based indicator of cooling and water status.
Key takeaways
- Leaf temperature responds quickly to VPD, solar radiation, soil water deficit, and plant transpiration.
- A well-watered, transpiring leaf can be cooler than ambient air.
- A drought-stressed or under-irrigated leaf can approach or exceed ambient air temperature.
- The LT-2T model is designed for leaf-to-air temperature difference measurements.
- SDI-12 output makes leaf temperature sensors suitable for data loggers, telemetry, and remote monitoring.
What is a leaf temperature sensor?
A leaf temperature sensor is a low-impact plant monitoring instrument used to measure the absolute temperature of a leaf. The Implexx leaf temperature sensor uses a sub-miniature touch probe: a high-precision glass-encapsulated thermistor held against the leaf by a lightweight stainless-steel wire clip.
Because leaf temperature is directly influenced by transpiration, radiation, humidity, air temperature, wind, and soil water availability, it provides a plant-based measurement for irrigation monitoring and plant physiology research.
How contact leaf temperature measurement works
The LT-1T leaf temperature sensor is an example of an clip-on style sensor.
A clip-on leaf temperature sensor places a small thermistor against the leaf surface. The sensor is typically installed on the lower, shaded side of the leaf blade to reduce direct radiation effects and allow the thermistor to equilibrate with leaf temperature. The sensor cable should be secured to the stem to reduce movement and improve long-term measurement stability.
1. Miniature thermistor contact
The thermistor contact area is about 1 mm², helping reduce disturbance to the natural temperature of the leaf.
2. Lightweight leaf clip
The clip and thermistor assembly weighs about 1.6 grams, making it suitable for long-term leaf-level measurements with minimal impact.
3. Fast measurement response
A short excitation and measurement time supports rapid detection of plant responses to changing environmental conditions.
Contact leaf temperature sensors vs infrared canopy temperature radiation (IRT) sensors
Contact leaf temperature sensors measure the temperature of the actual leaf surface using a miniature thermistor clipped directly to the leaf. This provides a highly targeted measurement with minimal influence from soil, canopy gaps, sun angle, or background radiation.
In contrast, infrared canopy temperature sensors measure thermal radiation remotely across a broader field of view, which may include leaves, stems, fruit, soil, and shaded areas. While infrared sensors are valuable for large-scale canopy screening, contact sensors are often better suited to leaf physiology, transpiration, stomatal conductance, and leaf-to-air temperature difference (LATD) studies where precise leaf-level temperature measurement is important.
Because contact sensors remain attached to the same leaf over time, they also provide strong consistency for long-term irrigation, drought stress, and plant response monitoring.
Leaf-to-air temperature difference (LATD)
The LT-2T leaf to air temperature sensor, available from Implexx, simultaneously measures leaf and ambient air temperature for LATD measurements.
Leaf-to-air temperature difference, often abbreviated as LATD, compares the temperature of a leaf with the temperature of the surrounding air or the leaf boundary layer. LATD is useful because it turns raw leaf temperature into a more interpretable signal of plant cooling, transpiration, and possible water stress.
Basic calculation
LATD = leaf temperature − air temperature
A negative LATD means the leaf is cooler than the surrounding air. A value near zero means leaf and air temperatures are similar. A positive LATD means the leaf is warmer than the surrounding air.
How to interpret LATD
When water is available and stomata are open, transpiration cools the leaf, so leaf temperature may sit below air temperature. Under low irrigation or drought stress, stomata tend to close, transpiration decreases, and leaf temperature may rise toward or above ambient air temperature.
For stronger LATD interpretation, measure air temperature close to the leaf rather than relying only on a distant weather station. The LT-2T model is designed for this by pairing a leaf surface temperature sensor with an air boundary layer temperature sensor.
Compare LT-1T and LT-2T leaf temperature sensors
Two model options support different measurement goals: absolute leaf surface temperature or paired leaf and nearby air boundary layer temperature for LATD.
| Model | Sensor configuration | Best for | Primary output |
| LT-1T | One temperature sensor clipped to the leaf | Leaf surface temperature, irrigation monitoring, plant physiology, general crop stress studies | Absolute leaf temperature |
| LT-2T | Two temperature sensors: one on the leaf surface and one measuring air boundary layer temperature | Leaf-to-air temperature difference, plant cooling, transpiration interpretation, water stress studies | Leaf temperature plus nearby air/boundary-layer temperature |
Applications of leaf temperature research & monitoring
Leaf temperature sensors support both practical crop management and scientific plant physiology, especially when combined with air temperature, VPD, radiation, soil moisture, sap flow, or stomatal conductance measurements.
Irrigation scheduling and water stress
Track plant temperature response to irrigation, drought, heatwaves, and soil water deficits.
Plant physiology research
Measure rapid leaf temperature responses to VPD, solar radiation, stomatal conductance, and transpiration dynamics.
Remote phenotyping and treatment comparison
Compare cultivars, irrigation strategies, canopy positions, greenhouse zones, or stress-response treatments over time.
Key leaf temperature sensor specifications
These specifications help users evaluate whether a contact leaf temperature sensor is suitable for field monitoring, controlled-environment research, or IoT deployment.
| Feature | Why it matters | Specification |
| Measurement range | Covers typical field and greenhouse leaf temperature conditions. | −5 to +50 °C |
| Accuracy / tolerance | Small differences matter when calculating LATD. | Accuracy <0.15 °C; tolerance range ±0.08 °C |
| Contact area | Small contact area minimizes leaf disturbance. | About 1 mm² |
| Leaf clip weight | Lightweight clips reduce measurement artefacts on the leaf. | 1.6 grams |
| Output | Digital output simplifies logger and IoT integration. | SDI-12; voltage or 4–20 mA available upon request |
| Input power | Low-power operation supports small batteries and remote stations. | 5 to 24 VDC |
| Measurement time | Fast response supports rapid plant-environment studies. | 0.15 seconds |
| Protection | Field sensors must tolerate wet operating conditions. | IP64 |
| Cable length | Long cables support flexible field installation. | 5 m standard; up to 75 m in datasheet / 60 m listed on product page |
Practical selection tip: Use the LT-1T when you need direct leaf surface temperature. Use the LT-2T when your core metric is leaf-to-air temperature difference, because it measures both leaf surface temperature and the nearby air boundary layer temperature.
Frequently Asked Questions
The Implexx range of leaf temperature sensors are ideal for scientific research and irrigation management.
What does a leaf temperature sensor measure?
It measures the absolute temperature of a leaf, usually by placing a miniature thermistor in contact with the leaf surface.
What is leaf-to-air temperature difference?
Leaf-to-air temperature difference is calculated by subtracting air temperature from leaf temperature. It indicates whether a leaf is cooler, similar to, or warmer than the surrounding air.
Why can leaves be cooler than air?
Leaves can be cooler than air when stomata are open and transpiration is actively removing heat through evaporative cooling.
Why can leaves become warmer than air?
Leaves can become warmer than air when water stress or low irrigation causes stomatal closure, reducing transpiration and evaporative cooling.
Where should the sensor be installed?
For contact measurements, install the thermistor on the lower, shaded side of the leaf and secure the cable to reduce movement.
However, placement may depend on leaf orientation and architecture. For example, amphistomatous leaves (i.e., leaves with stomata on both upper (adaxial) and lower (abaxial) surfaces) may require a leaf temperature sensor on both sides of the leaf or randomly distributed. Hypostomatous leaves (i.e., leaves with stomata predominately on the lower (abaxial) surface) may only require a leaf temperature sensor on the lower, shaded side of the leaf.
Is the sensor suitable for remote monitoring?
Yes. SDI-12 output, low power operation, and logger compatibility make the sensor suitable for telemetry, LoRaWAN, NB-IoT, and remote field monitoring.