Z991 FluorPen

Z991 FluorPen is a chlorophyll fluorescence measuring device for the lab and the field. This hand-held fluorometer uses high output LEDs to provide a saturating pulse for the measurement of Fv/Fm (QY) and other parameters. The Z991 FluorPen is an accurate, portable option to bulky fiber optic chlorophyll fluorometers, especially when the user wants to screen a large number of plants for specific fluorescence parameters.

Four different standard versions of FluorPen are available.  All measure Ft, QY and kinetic responses such as OJIP, NPQ and Light Curve responses of QY, but have either a built in standard leaf clip (Z991) or are adapted to be used with detachable leaf clips (Z991-D).  The Fluorpen can also be purchased with a build in PAR meter for measurements in 400-700nm range (Z991-LM or Z991-LM-D)

  • Ft – continuous fluorescence yield in non-actinic light. Ft is equivalent to Fo if the leaf sample is dark-adapted.
  • QY – Photosystem II quantum yield. In a dark-adapted leaf this is equivalent to Fv/Fm. In a light-adapted leaf it is equivalent to Fv‘/Fm‘.
  • OJIP – Chlorophyll Fluorescence Induction Kinetics (fast transient analysis) is a simple and non-invasive tool to monitor chloroplast function. Provided OJIP analysis is used as sensitive and reliable fast test for the functionality and vitality of photosynthetic system.
  • NPQ – Non-Photochemical Quenching.  Provided are two predefined NPQ protocols differing in the duration of light exposure and dark recovery phase as well as in the number of intervals between the pulses. It is typically used for quantification of photochemical and non-photochemical quenching in dark-adapted samples.
  • Light Curve – Adaptation of Quantum Yield to Several Different Light Levels.  There are three predefined Light Curve protocols based on pulse modulated fluorometry differing in number and duration of single light phases and light intensities. Light Curve protocols provide successive measurements of the sample photosynthesis under various light intensities of continuous illumination relating the rate of photosynthesis to photon flux density.

Measuring light power is adjustable by flash duration; actinic light is adjustable up to 1000 µmol photons/m2/s and saturating flashes are adjustable  up to 3,000 µmol photons/m2/s.

All FluorPens come with two data transfer options built in USB and Bluetooth and they all have a GPS module built in.  The FluorPen operates on Lithium battery that can be easily recharged via USB port. 


Z991 FluorPen is available with two style of leaf clip.  Standard leaf clip is attached to the device, and the removable leaf clip can be placed on  the leaf ahead of time for dark adaptation purposes.  An optional feature of the FluorPen is the PAR light meter (LM).  When included it is built in on the front panel of the device and it measures photosynthetically active radiation in 400-700nm range in units of umol photons/m2/s.  The list of available versions is as follows:

Z991  Standard leaf clip FluorPen

Z991-D FluorPen adapted for use with detachable leaf clips (10 leaf clips included)

Z991-LM Standard leaf clip FluorPen with PAR light meter built in

Z991-D-LM FluorPen adapted for use with detachable leaf clips (10 leaf clips included) and built in PAR light meter

In addition to the 4 standard Z991 FluorPen versions, two Monitoring Pen FluorPens are also available. These devices measure the same parameters as the standard FluorPens but are designed for use in different environments.   Z991-M-E is the Extended Monitoring Pen designed for extreme weather conditions and long term, unattended monitoring of chlorophyll fluorescence parameters in the field or in the lab. It features rugged weather proof case and may be ordered with features for remote (software control, data collection) or manual two button control and data collection to the device.  The second version of the Monitoring Pen Z991-M-A is the Aquatic Monitoring Pen and it has been designed for use under water (up to 2m depth).  The control of the Aquatic Monitoring Pen may be with the two buttons by the user or via remote software on the computer (maintained above the water level).  a customized version of the Z991-M-A may be provided for depths greater than 2m (contact Qubit Systems for details).

Z991-M-E Extended Monitoring Pen

Z991-M-A Aquatic Monitoring Pen

  • Hand held PAM chlorophyll Fluorometer
  • Different leaf clip options
  • Ideal for field, greenhouse and lab research
  • Built in GPS module
  • Rechargabel lithium battery
  • Both USB and BT data communication via PC software

NPQ and Light Curve Protocols

NPQ Protocol Includes Five Measurements in Actinic Light and three measurements during dark relaxation.

NPQ 1 protocol: light duration 60s, 5 pulses; dark recovery duration 88s, 3 pulses

NPQ 2 protocol: light duration 200s, 10 pulses; dark recovery duration 390s, 7 pulses


NPQ_Ln = (FM – FM_Ln) / FM_Ln

NPQ_Lss = (FM – FM_Lss) / FM_Lss

NPQ_Dn = (FM – FM_Dn) / FM_Dn


Formulas Derived From:

R.J. Strasser, A. Srivastava and M. Tsimilli-Michael (2000): The fluorescence transient as a tool to characterize and screen photosynthetic samples. In: Probing Photosynthesis: Mechanism, Regulation and Adaptation (M. Yunus, U. Pathre and P. Mohanty, eds.), Taylor and Francis, UK, Chapter 25, pp 445-483.

Explanation of OJIP Parameters:

  • Bckg = background
  • F0: = F50µs; fluorescence intensity at 50 µs
  • FJ: = fluorescence intensity at j-step (at 2 ms)
  • Fi: = fluorescence intensity at i-step (at 60 ms)
  • FM: = maximal fluorescence intensity
  • FV: = FM – F0 (maximal variable fluorescence)
  • VJ = (FJ – F0) / (FM – F0)
  • Vi = (Fi – F0) / (FM – F0)
  • FM / F0
  • FV / F0
  • FV/ FM
  • M0 or (dV / dt)0 = TR0 / RC – ET0 / RC = 4 (F300 – F0) / (FM – F0)
  • Area = area between fluorescence curve and FM (background subtracted)
  • Fix Area = total area above the OJIP fluorescence transient – between F40µ and F1s(background subtracted)
  • SM = area / FM – F0 (multiple turn-over)
  • Ss = the smallest Sm turn-over (single turn-over)
  • N = SM . M0 . (1 / VJ) turn-over number QA
  • Phi_P0 = 1 – (F0 / FM (or FV / FM)
  • Psi_0 = 1 – VJ
  • Phi_E0 = (1 – F0 / FM)) . Psi_0
  • Phi_D0 = 1 – Phi_P0 – (F0 / FM)
  • Phi_Pav = Phi_P0 – (SM / tFM); tFM) = Time to reach FM (in ms)
  • ABS / RC = M0 . (1 / VJ) . (1 / Phi_P0)
  • TR0 / RC = M0 . (1 / VJ)
  • ET0 / RC = M0 . (1 / VJ) . Phi_0)
  • DI0 / RC = (ABS / RC) – (TR0 / RC)


FluorPen Data capture screen

NPQ data capture screen

OJIP measurements capture screen

LIght Curve captrue screen