The Standard in

Plant Stress Measurement



The most advanced portable modulated chlorophyll fluorometer available, with FM'  correction option, according to Loriaux 2013, included for all light adapted protocols including quenching.

The OS5p+ portable system - includes the latest advancements in variable chlorophyll fluorescence measurements. The OS5p+ can measure most types of plant stress, and offers a wider range of up to date measuring protocols and automation.


  • Detection and Measurement of Most Types of Plant Stress
  • Designed to allow & measure chloroplast migration qM
  • Stable Internal Actinic Light Source for reliable field and laboratory quenching tests
  • Loriaux (2013) FM' Correction Option or Square Topped Saturation Flash for all light adapted techniques including quenching
  • PAR clip included - Measures PAR, leaf temperature, & ETR
  • Integrated GPS/GLONASS location receiver
  • 8 hour battery charge life
  • Option for automated modulated light set-up
  • Menu driven color graphic touch screen interface
  • Data output via USB port and removable SD memory card
  • Armored fiber optic light guide

Wide Range of Programmable Testing Protocols including:

  • Kramer lake model quenching
  • Hendrickson lake model quenching
  • Puddle model quenching
  • Quenching relaxation including direct readout of qE, qM, qT, qZ, & qI
  • Strasser OJIP & all of Strasser's measuring parameters
  • Vredenberg OJIP
  • Rapid light curves or RLC - includes: ETRmax, α, Ik, & Im  - with on screen curve fitting, allowing multiple overlays
  • Light curves
  • Y(II) with PAR, & ETR
  • FV/FM & FV/FO
  • The OS5p+ is designed to be the most advanced chlorophyll fluorometer available. It is intended for advanced plant research and plant stress measurement. It offers the latest updates in chlorophyll fluorescence capabilities, including: FM' correction according to Loriaux 2013, a stable white actinic white light source that allows chloroplast migration, and quenching relaxation measurement of qE, qT, qM, qZ, and qI. It also provides a comprehensive list of quenching protocols including Kramer lake model, Hendrickson lake model, and puddle model protocols. Other capabilities include: A Y(II) protocol, an FV/FM protocol, Strasser OJIP, Vredenberg OJIP, and Rapid Light Curves (for changing light conditions).

  • Parameters Measured and Protocols included:



    Quantum Photosynthetic Yield of PSII (or F/FM' or Y).


    Electron transport rate (w/optional clip).


    Photosynthetically Active Region value (with optional PAR clip).


    Leaf temperature (with optional PAR clip).


    Maximum Photochemical efficiency of PSII.


    A more sensitive detector of stress than FV/FM, but it does not measure plant efficiency.


    Minimum fluorescence.


    Maximal fluorescence.


    Variable fluorescence.

    FMS (or FM'):

    Maximal fluorescence with actinic illumination at steady state fluorescence.

    FS (or F):

    Fluorescence under steady state conditions (prior to saturation pulse).

    RLC (Rapid light curves):



    A measure of a leaf's photosynthetic capacity or maximum electron transport rate a is the initial slope of line at low PAR values created by relating ETR to PAR. It provides a measure of quantum efficiency.


    A measurement of the light intensity where light saturation dominates, or the minimum saturation level.


    PAR light intensity at ETRMAX.

    Quenching protocol:


    Hendrickson lake model quenching protocol:

    Y(NPQ), Y(NO), Y(II), NPQ, FV/FM.

    Kramer Quenching (standard):

    qL, Y(NPQ), Y(NO), Y(II), FV/FM.

    Puddle model parameters (standard):

    NPQ, qN, qP, Y(II), FV/FM.

    Quenching relaxation protocol (standard):

    qE, qM, qZ, qT, qI along with either puddle model, or Hendrickson parameters. Adjustable times for each.



    Up to 32 traces can be overlaid on the graphic display screen. The data file is designed for easy overlay graphing and spider plot graphing. Thousands of measurement parameter sets can be stored in a single data file for spider graphing. The number of data files are only limited by machine memory limits. FO is measured not estimated.

    OJIP - Vredenberg OJIP quenching protocol:


    OJIP - Strasser Protocol:

    Direct readout of: OJIP t100μs, t300μs (or K step), tFM (or time to P or FM), A (or area above the curve), MO (or RC/ABS), PIABS (or performance index).

    Strasser OJIP parameters reported to the data file only:


    Light Sources:


    Saturation pulse:

    White LED with 690 nm short pass filter. 15,000 μmols, 7,500 μmols with PAR clip.

    Modulated light:

    Red: 660 nm LED with 690 nm short pass filter.

    Actinic light source:

    RGB light source with adjustable spectra. Intensity adjustable up to 6,000 μmols.

    Far red light:

    720 nm LED with >700nm long pass filter.

    Detection method:

    Pulse modulation method.

    Detector & Filters:

    A PIN photodiode with a 700 ~ 750 nm bandpass filter.

    Sampling Rate:

    Auto-switching from 1 to 10,000 points per second, depending on test & on phase of test.

    Automated routine to optimally set the modulated light intensity. The modulated light may also be set manually.

    Multi-Flash FM' correction for all light adapted protocols & quenching. It may be turned on or off.



    Test Duration:

    Adjustable from .1 seconds to 12 hours.

    GPS location:

    Built in GPS / GLONASS 12 channel receiver with internal antenna.

    Storage Capacity:

    1 Gigabyte of non-volitile flash memory.

    Digital Output:

    USB removable storage device standard. Comma delimited files.

    SD/MMC data card.

    User Interface:

    640 x 480 graphic color touch screen.

    Menu driven touch screen.

    Power Supply:

    Internal 12V rechargeable nickel metal hydride battery.

    Battery Life:

    6 to 8 hours of continuous operation.


    7 in x 5.5 in x 3.25 in (17.8 cm x 14 cm x 8.3 cm).


    3.6 lbs (1.6 kg).

    Operating temperature:

    0 - 50oC, non condensing.

    Specifications subject to change without notice.

  • FL-DC

    Dark adaptation clip


    Pouch of 50 clips


    Adjustable locking desktop arm


    Large universal tripod - extends from 1.4m to 3.2m.


    70Ah Battey Belt

  • PDF document.

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Opti-Sciences, Inc.     8 Winn Avenue      Hudson NH 03051       USA      (603)883-4400

Opti-Sciences, Inc.

8 Winn Ave

Hudson, NH 03051, USA

Phone: (603) 883-4400

Fax: (603) 883-4410