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Universal Light Meter & Data Logger

The ULM-500 is a fast light meter / data logger with a high dynamic range and adequate optional PAR-sensors for independent PAR-measurements, PAR-monitoring or automated light list calibration of WALZ devices.

Our data logger and sensors are capable of resolving the saturating light pulse of PAM Chlorophyll Fluorometers or fast light flecks in nature.

Outstanding Properties of the ULM-500

  • Data logger with high data storage capacity
  • Multiple sensor can be read in parallel
  • PAR calibration for PAM devices
  • Low power consumption, long battery life

Outdoor use of the ULM-500.

General Features ULM-500

Light Measurement

The main purpose of the ULM-500 is light-measurement. The ULM-500 has two connectors for light sensors with BNC plugs. Typically, PAR sensors and pyranometers are linked to the ULM-500. PAR sensors measure the flux of quanta (unit, μmol m-2 s-1) in the photosynthetically relevant wavelength range, that is, between 400 and 700 nm. Pyranometers detect the power of radiation (unit, W m-2) mostly in a wider spectral range so that solar radiation arriving at the Earth’s surface can be measured. When power of radiation is measured, a flux of short-wavelength (e.g. blue) photon results in a higher signal than the same flux of photons with longer wavelengths (e.g. red) simply because the former flux carries more energy than the latter.

The higher energy in blue than in red photons, however, is unavailable for photosynthesis so that photon fluxes as they are measured by PAR sensors are important for photosynthetic studies. We offer three different PAR-sensors suitable for use in conjunction with the ULM-500. Please find more information on sensors by clicking here.

Dynamic Range

The ULM-500 has 5 sensitivity ranges with fast automatic switching. As a result it has a high dynamic range reaching up to 99 999 μmol m-2 s-1 and may detect signals down to 0.1 μmol m-2 s-1 – even with the smallest sensor we offer. The range-switching can be set to automatic for convenient measurements or to manual for fast time resolution.

High time resolution for the record of saturation pulses of PAM instruments (here the SP of a Phyto-PAM is shown).

Time Resolution – Chart Mode

Channel no. 1 of the ULM-500 is optimized for high time resolution. In the chart mode a time course of 1.2 s (or 2.4 s) is shown, which contains 120 data points (max. 100 Hz). The minimum, maximum and average are indicated. With the triggered chart function a saturating light pulse changing from dark to several thousand μmol m-2 s-1 can be resolved. This is usually not possible with standard light meters. The ULM-500 can be connected to the software WinControl-3 for continuous fast recording of light flecks.

Data Storage

The ULM-500 can be used as simple light meter for single light measurements or as data logger for continuous measurements. It can store up to 50 000 data points. Stored data can be downloaded with the software WinControl-3.


The ULM-500 has two BNC-connectors for light or PAR-sensors. Furthermore it has one connector for the Monitoring Leaf-Clip JUNIOR-B (Gen.1, analogue version), which can also be used to connect the Leaf-Clip 2030-B via an additional adapter (not compatible to 2035-B).
With the leaf clips not only PAR but also leaf temperature is measured, recorded and displayed.


The ULM 500 can be operated with its internal batteries or power can be supplied via USB-connector. Display illumination with white LED backlight renders readability in the dark. The ULM-500 is a stand-alone instrument, but can also be connected to a computer and operated with the software WinControl-3. Storage of several sensor calibration data is possible (10 different calibration values with probe names via WinControl-3 software).