ULM-500 Light Meter & Logger
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Universal Light Meter & Data Logger
Measuring Photosynthetically Active Radiation for Plant Science
The ULM-500 is a universal light meter and data logger for measuring photosynthetically active radiation (PAR) in air and water. PAR - the photon flux between 400 and 700 nm - is the light that drives photosynthesis and is the most important physical parameter for any plant science experiment involving light.
The ULM-500 measures PAR with a time resolution of up to 100 Hz, a dynamic range spanning five orders of magnitude, and automatic range switching. This makes it fast enough to resolve the saturating light pulses of PAM chlorophyll fluorometers and sensitive enough to capture fast light flecks in natural canopies.
High Dynamic Range for Natural Light and Saturation Pulses
The ULM-500 has 5 sensitivity ranges with fast automatic switching, covering a dynamic range from 0.1 to 99,999µmol m⁻² s⁻¹ even with the smallest PAR sensor available. Range switching can be set to automatic for convenient measurements or to manual for maximum time resolution.
PAR Sensors for Every Measurement Geometry
The ULM-500 works with three types of PAR sensors, each designed for a different measurement geometry: The MQS-B Cosine Corrected Mini Quantum Sensor measures photosynthetic photon flux density (PPFD) on flat surfaces with cosine-corrected angular response - the standard photosynthetically active radiation sensor for field and laboratory use. The US-SQS/L Spherical Micro Quantum Sensor measures photon fluence rate omnidirectionally in suspensions and underwater . ideal for algae cultures and aquatic research. The LS-C Mini Quantum Sensor is a compact, waterproof sensor for versatile PAR measurements in tight spaces.
Resolving Fast Light Changes at Up to 100 Hz
Channel 1 is optimized for fast acquisition. In chart mode, a 1.2-second time course with 120 data points is displayed, showing minimum, maximum, and average. The triggered chart function resolves saturation pulses from dark to several thousand µmol m⁻² s⁻¹, usually not possible with standard light meters. Connected to WinControl-3, the ULM-500 provides continuous fast recording of light flecks in natural environments.
Built-In Data Logger with 50,000 Data Points
The ULM-500 stores up to 50,000 data points in its internal flash memory. In automated logging mode with sleep function (e.g. one measurement every 5 minutes), batteries last 3- 4 months. Stored data can be downloaded via the WinControl-3 software for analysis or export to spreadsheet programs.
How the ULM-500 Is Used in Practice
Stand-Alone Light Measurement
The ULM-500 operates independently as a PAR sensor with data logger - no computer required. An internal timer triggers continuous measurements at user-defined intervals. The sleep mode minimizes power consumption for long-term field deployments.
Calibration of PAM Instruments
For Walz PAM fluorometers and the IMAGING-PAM system, the ULM-500 provides automated light list calibration and real-time monitoring of actinic and saturation pulse intensities. The high time resolution ensures accurate characterization of even the fastest light pulses.
Attenuation Index
With two BNC connectors for parallel data acquisition, the ULM-500 can calculate an attenuation index using two identical PAR sensors above and below a sample — useful for canopy transmittance studies and leaf area index estimation.
