Photosynthesis is driven primarily by photos of light with wavelengths between 400 and 700 nanometers, which is referred to as Photosynthetically Active Radiation, or PAR light which is used for PAR mapping. Because a quantum is the amount of energy possessed by a photon, PAR light is sometimes labeled quantum light. The intensity of PAR light is referred to as Photosynthetic Photon Flux Density (PPFD), which is measured in units of µmol m-2 s -1 (the number of photons, in units of micromoles, striking an area one meter square each second). Quantum Light Meters are calibrated to display PPFD.  Measuring quantum light can tell you if your plants are getting a sufficient amount of usable light.
As you can see from the curve below, the original non LED sensors (in black) don’t allow for the measuring to include the complete spectrum of the McCree Curve.  The full spectrum LED sensor (in gold) fills almost the entire curve.
Full Spectrum:  Features an improved detector that provides excellent measurements under all light sources, including LEDs, right out of the box.
Original:  A lower-cost option that is excellent for all light sources, except most LEDs, where post-measurement correction factors need to be applied to achieve accurate readings
PAR Meters (also known as Light meters or Quantum meters) continue to evolve as demand raises.  You need to understand what you’re buying before laying out the bucks for equipment. This is why we are sharing some important information on four different PAR meters to help people more easily decide what to purchase based on their needs.




Li-Core Li-190R
Apogee MQ 200
Spectrum Technologies Light Scout 3415F
Gigahertz Optik MSC15




LiCore PAR meter
Features – Quick Peek
Design and Accessories
The LI-190R Quantum Sensor measures Photosynthetically Active Radiation (PAR, in µmol of photons m-2 s-1). It provides accurate measurements—in the open, in greenhouses, under plant canopies, or in growth chambers—for most broad-spectrum light sources, including natural sunlight, artificial, or mixed sources.
▪ Uniform sensitivity across the PAR waveband foraccurate measurements outdoors, under vegetation,or in artificial lighting without changing the calibration
▪ Newly designed optical filter tailors the spectralresponse to an unprecedented performance standard
▪ Weather resistant and durable in high-temperature,high-humidity, long-term deployments
▪ Cosine correction is accurate even when the lightsource is not directly overhead
▪ Sensor heads are detachable and interchangeablefor simplified installation, removal, and recalibration
Spectral analysis
The LI‑190R uses a high-quality silicon photodiode and glass optical filter to create uniform sensitivity to light between 400 nm to 700 nm, which closely corresponds to light used by most plants. A newly designed optical filter tailors the spectral response to an unprecedented performance standard. Furthermore, the new filter is unaffected by environmental factors such as heat or humidity. The filter blocks light with wavelengths beyond 700 nm, which is critical for measurements under vegetation where the ratio of infrared to visible light may be high.
The sensor features excellent cosine response, which ensures accurate measurements under diffuse light and when sunlight originates from a low solar angle. This, in combination with high resolution at low light levels, makes the LI-190R useful for determining the light compensation point in plants.
Data logging
Intuitive, menu-driven interface.  The menu-driven interface is easy to use. Attach your LI‑COR light sensor(s) to the three BNC connectors. Log manually or use menus to set up one-time, daily, or continual measurement routines. Sampling rates and logging intervals are user-selectable.
$470.00 – $485.00



Features – Quick Peek
Design and Accessories 
The MQ-200 has a hand-held meter, attached via cable to an anodized aluminum housing that displays in real time and stores measurements. The sensor head features a fully potted, domed-shaped design making it fully waterproof, weatherproof and self-cleaning.   Sensors are available as line quantum sensors (multiple detectors mounted along the length of a rugged anodized aluminum bar), which provide spatially averaged PPFD measurements along the length of the bar. All sensors in the line are electrically connected, resulting in a single voltage output that is directly proportional to average PPFD.
Accurate, Stable Measurements – Calibration in controlled laboratory conditions is traceable to an NIST lamp.Quantum sensors are cosine-corrected, with directional errors less than ± 5 %at a solar zenith angle of 75°. Long-term non-stability determined from multiplereplicate quantum sensors in accelerated aging tests and field conditions is less than 2 % per year
Rugged, Self-cleaning Housing – Patented domed shaped sensor head (diffuser and body) facilitate runoff of dewand rain to keep the sensor clean and minimize errors caused by dust blocking the reduced path. Sensors are housed in a rugged anodized aluminum body and electronics are fully potted.
Spectral analysis
Typical applications include PPFD measurement over plant canopies in outdoor environments, greenhouses, and growth chambers, and reflected or under-canopy (transmitted) PPFD measurements in the same environments.
  • Spectral Range 410 to 655 nm (wavelengths where response is greater than 50 % of maximum.
  • Directional (Cosine) Response ± 5 % at 75º zenith angle (see Cosine Response below)
  • Temperature Response 0.06 ± 0.06 % per C (see Temperature Response below)
Data logging
The Apogee Mq-200 can store up to 99 manual measurements at one time, using the SMPL mode. Using the LOG mode, the meter will automatically take a measurement every 30 seconds. This is a great feature unique to the Apogee Mq-200. The meter will even turn itself on/off during this time to conserve battery. These values are viewable on the LCD screen, and also downloadable for external analysis.
Downloading data to a computer requires the AC-100 communication cable (a standard USB cable will not work) and ApogeeAMS software.



Light Scout PAR Meter
Features – Quick Peek
Design and Accessories
Individual light sensors, available individually or as a bar of 3 or 6 sensors, allow you to measure site-specific areas. These hand-held sensors feature cosine correction, built-in levels, and mounting brackets for stationary measurements.  Light Bars are frequently used when measuring across a greenhouse bench.
Spectral analysis
LightScout Quantum Light Meters are calibrated for sunlight. Due to differences in the spectrum generated by artificial lights, the following adjustments must be made in the value shown on a sunlight-calibrated meter:
  • Fluorescent: reads 8% high, so multiply the display by 0.92.
  • Metal Halide: reads 6% high, so multiply the display by 0.94.
  • High Pressure Sodium: 0% error—no adjustment needed.
  • Sunlight: 0% error—no adjustment needed.
Light Bars take the average light reading for multiple sensors across a fixed length. This can be used to determine canopy density and light transmission.
  • Measures photosynthetically active radiation (PAR) from 400 to 700 nm
  • Range of 0 to 2,000 µmol·m-2·s-1

Data logging

Data logging not included
199.00   LightScout Quantum Meter (3415F)
279.00  LightScout Light Sensor Reader comes with 6 ft (2m) cable
219.00   LightScout Quantum Light Sensor
315.00   LightScout Quantum Light 3 Sensor Bar



Features – Quick Peek
Design and Accessories
Handheld meter for illuminance and light color. Integrated sensor with Color-Touchscreen, simple intuitive operation with clearly arranged display views.
Besides being compact and durable, an additional function of the MSC15 is the display of Photosynthetic Photon Flux Density (PPFD) in µmol/m²s (400 nm to 700 nm) which is a measure of the total number of photons within the PAR wavelength range that reach a surface each second per square meter area.
One essential quality feature of photometric devices is their precise and traceable calibration. The MSC15 is calibrated by Gigahertz-Optik’s calibration laboratory that is accredited by DAkkS (D-K-15047-01-00) for the spectral responsivity and spectral irradiance according to ISO/IEC 17025. Every device is supplied with its respective calibration certificate.
Light measurements
The MSC15 is the display of Photosynthetic Photon Flux Density (PPFD) in µmol/m²s (400 nm to 700 nm) which is a measure of the total number of photons within the PAR wavelength range that reach a surface each second per square meter area.
spectral range between 360 nm and 830 nm
optical bandwidth correction feature (CIE 214)
Data logging
Software CD and development kit for integration of the device in the user’s own software
Gigahertz-OptikMSC15 software
Not yet determined



Donna Ebeling About Donna Ebeling

Gardening had always been my passion, until I learned about organic gardening. That’s a whole new ballgame. So when I was asked to write for this blog, I jumped at the opportunity to research, to learn more about organic gardening and to write about that and other plant-related topics. Thank you for being here, I hope you enjoy these articles at least half as much as I do writing them!