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Environmental measurement & analysis
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Small sensors


The ML-series small sensors are used as multi-purpose cost effective sensors for qualitative radiation measurements in the fields of photovoltaics, horticulture, agriculture and industry. Those compact all-weather sensors rely on a passive high quality detector. Based on the integral construction of each sensor type, irradiance (W/m2), illuminance (Lux) or photosynthetic photon flux density (µmol/m2/s) can be measured. All sensors have an optical quality glass dome which minimizes the soiling of the diffusor and optimizes the cosine response.  Within the operating temperature range, the ambient temperatures has a rather small effect on the sensor output and makes it a reliable sensor under varying environmental conditions. The compact dimensions of the sensor body make it easy to integrate to any type of applications. For mounting the sensor in an horizontal position, an optional mounting plate is available.


Product Model Description
ML-020P PAR Sensor

ML-020P PAR Sensor

The compact ML-020P PAR sensor or Quantum sensor has a special opical filter to mimic the spectral …

ML-020S Lux Sensor

ML-020S Lux Sensor

The MS-020S-O and ML-020S-I illuminance sensors are both all-weather sensors having customized detector …

ML-01 Si-Pyranometer

ML-01 Si-Pyranometer

The ML-01 Si-sensor is the link between the reference cell and broadband thermopile pyranometer. Compared …




    Lux Sensor       


    Lux Sensor       


PAR Sensor



   High illuminance Low illuminance    

Spectral response

CIE Photopic Curve

Photon Flux Density

400 - 700 nm

(400 to 1100nm)

Measuring range

~ 150,000

~ 30,000

~ 3000











~ 50mV

Internal resistance





Temperature response

(-10 to +50°C)




< 0.15 %/°C

Directional response

(@ 30/60/80°)


1 / 1.5 / 17 %


< 10 W/m²

Spectral error





Output cable

5m, standard



Light pollution and straylight monitoring

Light pollution and straylight monitoring

Light pollution is a delicate issue in highly populated areas (large cities and industrial areas). Since light pollution can have a strong impact on life, the live of animals can be ...

Stability monitoring of Sun simulators

Stability monitoring of Sun simulators

Stability monitoring of a sun simulator enables the reseracher to improve the stability of the PV cell and precision of the of the I-V measurement. With the MP-180, which is a dedicated ...

Measuring Photon Active Radiation (PAR)

Measuring Photon Active Radiation (PAR)

Photon active radiation is defined in the spectral range 400nm and 700nm expressed in mole of photons per square meter per second. Photo active radiation is an important measure to ...

Calibration Procedure & Traceability

The sensor is calibrated against an identical calibrated reference sensor using a 1000 W/m2 Class AAA sun simulator as source. The test sensor is placed on a horizontal table and aligned to the optical axis of a normal incidence light source. By alternating the position of the calibrated reference sensor with the test sensor, the output signal of both sensors is recorded and used to solve the equation of the unknown sensitivity variable. Since the operating conditions are relatively constant (e.g. ambient temperature and normal incidence irradiance), the sensor uncertainty figure is determined by taking into account the sensitivity uncertainty of the reference sensor and the max. deviation of the incident irradiance between two measurement intervals.

Frequently Asked Questions

Soiling effect versus measured irradiance

Soiling effect versus measured irradiance

What is the effect of soling versus the measured irradiance? Measuring solar radiation with pyranometers, pyrheliometers or spectroradiometer, soiling has will have an effect ...

Re-calibration interval of solar sensors

Re-calibration interval of solar sensors

The sensitivity of the solar sensor will slightly deviate with time when it is exposed to solar radiation. Therefore it is advised to re-calibrate the sensor every two years. For calibration ...