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Enabling better global research outcomes in soil, plant & environmental monitoring.

LSM Light Sensor Meter for PAR Sensors

The LSM Light Sensor Meter is designed to continuously monitor photosynthetically active radiation (PAR).

The LSM Light Sensor Meter is most commonly used to monitor plant canopy light interception. A point PAR sensor, such as Apogee’s SQ-110, is installed above the plant canopy to measure ambient light conditions. Within and beneath the canopy, one or more LINPAR linear PAR sensors can be installed. This way, the fraction of absorbed radiation or leaf area index can be calculated.

The LSM Light Sensor Meter has an internal lithium ion battery which is charged by an external solar panel. The unit is IP65 rated and can tolerate all weather conditions encountered in the field. All data is logged to an internal 4GB MicroSD card which can be downloaded as a csv file. Data can also be downloaded via the internet if used in combination with the ICT Universal Telemetry Hub.

  • The LSM is a stand-alone instrument and does not have extensive cabling and power requirements. All data is stored within the unit on a removable MicroSD card.
  • Communication with the LSM is made either with a USB or wireless connection. Wireless is capable of a range of up to 250m.
  • The LSM has a Windows and Mac compatible configuration software. The software is GUI based and extremely user friendly. Custom calibration equations or data can be entered and edited via the software. Real-time measurements, diagnostics and sensor configuration can easily be made.
  • The LSM has 2 wire, non-polarised bus for power input. There is no chance of incorrect wiring of positive and negative voltage because the LSM is non-polarised.
  • The LSM has an internal lithium-polymer battery that is kept charged by an external power supply (solar panel or mains). The instrument has an internal voltage regulation for maximum power reliability.
  • The LSM is IP65 rated and has been demonstrated to operate in extreme environmental conditions. Units are being used in diverse environments from hot Australian deserts, tropical Amazon rainforests, temperate German forests, Indian agricultural fields and North American Arctic cold.


   LSM Diagram2

LSM – Virtual Sensor

The LSM automatically calculates the fraction of intercepted PAR ( f ).

The measurement of f is an indicator of a plant’s light use efficiency or its ability to convert sunlight into biomass. The simple method (see equation in diagram to right) requires at least one PAR sensor above the canopy to measure direct beam and two or more LINPAR sensors beneath the canopy (see diagram top right).

The complex method (see equation in diagram to right) also accounts for reflectance from the canopy and ground which can account for up to 5% of f.

  LSM PAR Graph

A LINPAR is necessary beneath or within a canopy because it samples a larger area and takes into account sunlight variability caused by the canopy. Plotting f over a growing season against some measure of yield or biomass indicates the light use efficiency of two or more crops.

Instrument Logging

Analogue Channels 10 single ended
Resolution 0.00001V—24-Bit
Accuracy 0.001V
Minimum Logging Interval 1 second
Delayed Start Suspend Logging, Customised Intervals
Sampling Frequency 10Hz


Communications USB, Wireless Radio Frequency 2.4 GHz
Data Storage MicroSD Card, SD, SDHC & SDXC Compatible (FAT32 format)
Software Compatibility Windows 8, 8.1 & 10; Mac.
Data Compatibility FAT32 compatible for direct exchange of SD card with any Windows PC
Data File Format Comma Separated Values (CSV) for compatibility with all software programs
Memory Capacity Up to 16GB, 4GB MicroSD card included.

Operating Conditions

Temperature Range -40°C to +80°C
R/H Range 0-100%
Upgradable User Upgradeable firmware using USB boot strap loader function


Internal Battery Specifications
960mAh Lithium Polymer, 4.20 Volts fully charged
External Power Requirements
Bus Power 8-30 Volts DC, non-polarised, current draw is 190mA maximum at 17 volts per logger
USB Power 5 Volts DC
Internal Charge Rate
Bus Power 60mA – 200mA Variable internal charge rate, maximum charge rate of 200mA active when the external voltage rises above 16 Volts DC
USB Power 100mA fixed charge rate
Internal Power Management
Fully Charged Battery 4.20 Volts
Low Power Mode 3.60 Volts – Instrument ceases to take measurements
Discharged Battery 2.90 Volts – Instrument automatically switches off at and below this voltage when no external power connected.
Battery Life varies
Example A: With a recommended solar panel and/or recommended power source connected, operation can be continuous.
Example B: Power consumption is dependent on number and type of sensors connected, frequency of measurement and measurement duration
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