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.
|Analogue Channels||10 single ended|
|Minimum Logging Interval||1 second|
|Delayed Start||Suspend Logging, Customised Intervals|
|Communications||USB, Wireless Radio Frequency 2.4 GHz|
|Data Storage||MicroSD Card, SD, SDHC & SDXC Compatible (FAT32 format)|
|Software Compatibility||Windows 7, 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.|
|Temperature Range||-40°C to +80°C|
|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|
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.
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.