Why Weather Sensors Show Higher Temperatures in Sunlight

Related Product： IOT-S300WS8 IOT-S300WS7

A Field Test on the “Temperature Accumulation Effect”

Accurate air temperature measurement is critical for environmental monitoring, agriculture, smart cities, and building automation systems. However, many outdoor sensors suffer from a hidden problem: temperature readings that rise artificially under strong sunlight.
This phenomenon, often called the temperature accumulation effect, can cause sensors to report temperatures 2–5°C higher than the actual ambient air temperature.
In this article, we share a real-world comparison test that reveals how this issue occurs and how an optimized sensor design can minimize its impact.

The Background: A Customer Comparison Test

The investigation started with feedback from a customer who compared two sensors:
  • A Linovision IOT-S300WS7 seven-in-one environmental weather sensor 
  • A six-parameter weather sensor from another manufacturer
The two devices were installed side by side on a balcony.
To the customer’s surprise, the sensors reported very different temperature values during the daytime. Since the other sensor had been used for a long time without any noticeable problems, the customer questioned whether our device might be inaccurate.
To resolve the issue objectively, our engineering team conducted a controlled comparison test.

Test Setup

To ensure reliable results, both sensors were installed under identical conditions:
  • Same outdoor test location
  • Same installation height
  • Same exposure environment
  • Same sampling time
Data was collected using a 4G multi-channel data acquisition system, ensuring synchronized measurements.
The test ran continuously for 24 hours.

Test Results

After compiling the temperature data, the trend showed a clear pattern.

Nighttime (00:00 – 09:25)

Both sensors reported almost identical readings.
This confirms that under low solar radiation, both sensors measure ambient air temperature accurately.

Daytime (10:00 – 16:00)

As solar radiation increased, the difference between the sensors grew significantly.
Observations included:
  • Temperature differences exceeding 2°C
  • Maximum difference reaching 5°C
  • The competing sensor consistently reporting higher temperatures
This pattern strongly indicates that one sensor was affected by solar heating rather than actual air temperature changes.

What Causes the Temperature Accumulation Effect?

The temperature accumulation effect occurs when the sensor body absorbs heat from the surrounding environment.
Common causes include:
  • Direct solar radiation
  • Ground-reflected heat
  • Poor airflow around the sensor
  • Inadequate radiation shielding
When the sensor housing heats up, the temperature probe measures the heated enclosure instead of the surrounding air.
This leads to systematic measurement errors, particularly during midday.

Engineering Solutions to Reduce Solar Heating

To address this challenge, modern weather sensors incorporate several design improvements.

  1. Radiation Shield Structure

A multi-layer radiation shield (similar to a Stevenson screen) blocks direct sunlight while allowing airflow.

  1. Breathable Waterproof Materials

Specialized materials protect the sensing element from moisture while maintaining air exchange.

  1. Thermal Isolation Design

Internal components are designed to minimize heat conduction from the sensor housing to the temperature probe.
These improvements ensure the sensor measures true ambient air temperature, even under strong sunlight.

Independent Validation

To confirm the findings, additional comparison tests were conducted using imported reference sensors.
The results were consistent:
  • The optimized sensor maintained stable temperature readings
  • The other sensor showed sunlight-induced temperature drift
Interestingly, the issue had not been detected previously simply because no direct comparison test had been conducted.

Key Takeaways

  • Solar radiation can cause outdoor weather sensors to report temperatures several degrees higher than actual air temperature.
  • This issue often goes unnoticed without side-by-side comparison testing.
  • Proper radiation shielding, ventilation, and thermal design are essential for accurate temperature measurement.
  • Well-designed environmental sensors can significantly reduce solar heating errors.

Frequently Asked Questions

Why do some weather sensors read higher temperatures in sunlight?

Direct solar radiation can heat the sensor housing. When the enclosure becomes warmer than the surrounding air, the temperature probe records the heated surface temperature instead of ambient air temperature.

What is the temperature accumulation effect?

The temperature accumulation effect refers to heat buildup in a sensor caused by solar radiation or reflected heat, leading to inflated temperature readings.

How can weather sensors avoid solar heating errors?

Common solutions include:

  • Radiation shields
  • Ventilated sensor housings
  • Breathable waterproof materials
  • Thermal isolation design
These methods help ensure the sensor measures true air temperature rather than solar-heated surfaces.

How large can the measurement error be?
In strong sunlight, poorly protected sensors may show errors of 2°C to 5°C or even higher.