Innovative Design

With an eye toward innovation, we’ve redesigned every aspect of the LI-6400XT so that the LI-6800 will be a valuable investment for years to come. The Dynamic Assimilation™ Technique (DAT) is based on a reformulation of the traditional assimilation equation. DAT allows measurements when chamber conditions are not at steady state, meaning that you can record faster CO2 response curves and survey measurements.

LI-6800 Fluorometer

Automatic water vapor control

Unlike the LI-6400/XT, the LI-6800 can humidify or dry the air stream independently of flow rate. The instrument rapidly adjusts to whatever humidity setting you specify and precisely controls water vapor over the course of a measurement. With more humidity control flexibility, you can make more precise vapor pressure difference (VPD) measurements.

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The Dynamic Assimilation™ Technique

When recording CO2 response curves using steady-state measurements, each point may take 90 to 120 seconds, requiring up to 35 minutes to record sufficient data to estimate the maximum velocity of carboxylation (Vc,max) and maximum rate of electron transport (Jmax). The Dynamic Assimilation™ Technique (DAT), however, provides comparable data in a fraction of the time.

Figure 1. Soybean CO2 response curve data from comparing DAT and steady state measurements. A-Ci curves collected using DAT have higher-density data and take less time than those collected using standard steady-state methods. Highlighting the time saving potential, the 400 ppm/minute curve was collected in 4 minutes and the 200 ppm/minute curve was collected in 8 minutes. In contrast, data for steady state curves may take up to 35 minutes to collect under ideal circumstances.

The LI-6800 features high air flow rates, excellent mixing of sample air, and minimal tubing between the infrared gas analyzers and leaf chamber, which in turn, provide high-speed measurements and fast response times.

This combination of features enables a reformulation of the assimilation equation such that steady state conditions are not a strict prerequisite for accurate gas exchange measurements. The new method is called the Dynamic Assimilation™ Technique.

DAT is superior to the RACiR (Rapid A-Ci Response) technique and steady-state measurements in several fundamental ways.

  • Eliminates the empirical empty chamber measurement and post processing required by RACiR.
  • Faster measurements – provides high-density CO2 response curve data in less time than traditional steady-state measurements.
  • Uncompromised data quality – data collected with DAT are comparable to traditional steady-state measurements.

Read more about the technique in this recent publication:

Saathoff, A. J., & Welles, J. (2021). Gas exchange measurements in the unsteady state. Plant, Cell & Environment, 44(11), 3509-3523.

Fast survey measurements

Make a survey measurement in less than a minute. The system’s fully automated control of the leaf environment is fast and responsive, achieving stability in as little as 45 seconds, so you can get more data out of your day.

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Advanced fluorometer

The Multiphase Flash Fluorometer measures both modulated and continuous fluorescence signals, delivering saturation flashes at intensities of 16,000 mol m-2 s-1 over a 6 cm2 leaf area. With high modulating frequencies (up to 250 kHz), the LI-6800 fluorometer can fully characterize the fluorescence induction transient (also called an “OJIP curve”) of a leaf at high resolution. The LI-6800 is the only combined gas exchange and fluorescence system to offer this feature.

Highly uniform light sources

The light sources are highly uniform, which means your leaf will experience more consistent assimilation. Variation in light intensities is less than 10% of the mean over 90% of the leaf area of the LI-6800 fluorometer. This high uniformity minimizes artifacts that can cause errors in gas exchange measurements and confound the understanding of processes that require comparison of gas exchange and PAM chlorophyll a fluorescence parameters.

Options for leaf area

From large sunflower leaves to small grasses, you have options for measurable leaf area. For very big leaves, a 6x6 cm chamber is available with the new Large Leaf and Needle chamber. The large leaf chamber aperture minimizes edge effects and maximizes signal-to-noise ratios.

For smaller leaves, choose the leaf area size of your Clear-top chamber. To fill the chamber area—and easily calculate leaf area—simply swap in one of three interchangeable apertures for different leaf areas: 3x3 cm, 2x3 cm, and 1x3 cm. On the Multiphase Flash Fluorometer, choose between 6-cm2 or 2-cm2 leaf area apertures.

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Dual light source control

With an additional cable and light source, it’s now possible to add a light source below the plant—in addition to the light source above the plant—to evenly illuminate the entire sample area. This also helps light both sides of thick plant material like cacti.

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If you do not receive it within 24 hours or if you have any questions, please contact LI-COR at 1-402-467-3576.

Bluestem Operating System

Designed with efficiency in mind, the Bluestem OS brings unprecedented clarity to your gas exchange and chlorophyll fluorescence measurements. Graphical illustrations show the configuration of each control and the status of feedback loops, helping you optimize each setting. This, in turn, saves time, increases understanding, and improves the quality of the measurements. Full color graphs, real-time data values, and status alerts all work together to ensure your measurements are the best that they can be. Once you have finished taking measurements, you can review data on the console or quickly download files to your computer for further analysis.

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Optimized volume, flow rate, and flow path

Good mixing in the sample volume, high flow rates, and proximity of gas analyzers to the sample volume combine to provide a highly accurate photosynthetic assimilation measurement and fast response time. This new document describes why the instrument is designed this way and it gives data to show how the system performs when compared to one with a smaller volume and lower flow rate.

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Interested in seeing more of the differences?

Interested in seeing more of the differences?

Download the complete list. Download the complete list.

Easy to learn, easier to use

With the LI-6400, researchers often spent weeks teaching new students how to configure the instrument. With the LI-6800, your students will be ready to collect data after a brief introduction. The intuitive graphical interface makes the controls easy to understand and easy to adjust. Now you can spend your time answering research questions, rather than learning an arcane instrument.

The full color display helps you visualize the instrument settings, making it easy to understand the instrument. Advanced graphing capabilities enable you to see data as measurements progress.


LI-COR offers photosynthesis training courses, so you can learn from the experts—including scientists who helped design the LI-6800—and get the tips and tricks that will turn you into a power user. Whether you are new to gas exchange and chlorophyll fluorescence or a seasoned expert, training courses will help you get the most out of your instrument, so you can get the most out of your time.

Studying Invasive Species with the LI-6800

“The LI-6400 is a great machine, but all the little tweaks you made to the LI-6800 improved the usability of it. The speed is great.”

– Randy Long, University of California Santa Barbara

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Gas Exchange and Fluorescence

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