Radiation that drives photosynthesis is called photosynthetically active radiation (PAR) and is typically defined as total radiation across a range of 400 to 700 nm. PAR is often expressed as photosynthetic photon flux density (PPFD): photon flux in units of micromoles per square meter per second (µmol m-2 s-1, equal to microEinsteins per square meter per second) summed from 400 to 700 nm (total number of photons from 400 to 700 nm). While Einsteins and micromoles are equal (one Einstein = one mole of photons), the Einstein is not an SI unit, so expressing PPFD as µmol m-2 s-1 is preferred.
Sensors that measure PPFD are often called quantum sensors due to the quantized nature of radiation. A quantum referes to the minimum quantity of radiation, one photon, involved in physical interactions (e.g., absorption by photosynthetic pigments). In other words, one photon is a single quantum of radiation.
Apogee Instruments SQ series quantum sensors consist of a cast acrylic diffuser (filter), photodiode, and signal processing circuitry mounted in an anodized aluminum housing, and a cable to connect the sensor to a measurement device. Sensors are potted solid with no internal air space. SQ series sensors output an analog voltage that is directly proportional to PPFD under sunlight (e.g., model SQ-110) or electric lights (e.g., model SQ-120).
| SQ-110/120 | SQ-212/222 | SQ-214/224 | SQ-215/225 | SQ-300 Series | SQ-420 | SQ-421 | SQ-422 | |
|---|---|---|---|---|---|---|---|---|
| Power Supply | Self-powered | 5 to 24 V DC | 7 to 24 V DC | 5.5 to 24 V DC | Self-powered | 5 V USB power source | 5.5 to 24 V DC | 5.5 to 24 V DC |
| Current Draw | - | 10 µA | 22 mA maximum; 2 mA quiescent | 10 µA | - | 61 mA when logging | 1.4 mA (quiescent); 1.8 mA (active) | RS-232 quiescent 36.87 mA, active 37.06 mA; RS-485 quiescent 37.37 mA, active 42.30 mA |
| Output (Sensitivity) | 0.2 mV per µmol m-2 s-1 | 0.625 mV per µmol m-2 s-1 | 0.004 mA per µmol m-2 s-1 | 1.25 mV per µmol m-2 s-1 | 0.2 mV per µmol m-2 s-1 | - | - | - |
| Output Type | 0 to 800 mV | 0 to 2.5 V | 4 to 20 mA | 0 to 5 V | 0 to 800 mV | USB | SDI-12 | Modbus |
| Resolution | - | - | - | - | - | 0.1 µmol m-2 s-2 | - | - |
| Calibration Factor (reciprocal of sensitivity) | 5 µmol m-2 s-1 per mV | 1.6 µmol m-2 s-1 per mV | 250 µmol m-2 s-1 per mV | 0.8 µmol m-2 s-1 per mV | 5 µmol m-2 s-1 per mV | Custom for each sensor and stored in the firmware | Custom for each sensor and stored in the firmware | Custom for each sensor and stored in the firmware |
| Calibration Uncertainty | ± 5 % | ± 5 % | ± 5 % | ± 5 % | ± 5 % | ± 5 % | ± 5 % | ± 5 % |
| Measurement Repeatability | Less than 0.5 % | Less than 0.5 % | Less than 0.5 % | Less than 0.5 % | Less than 0.5 % | Less than 0.5 % | Less than 1 % | Less than 1 % |
| Long-term Drift | Less than 2 % per year | Less than 2 % per year | Less than 2 % per year | Less than 2 % per year | Less than 2 % per year | Less than 2 % per year | Less than 2 % per year | Less than 2 % per year |
| Non-linearity | Less than 1 % (up to 4000 µmol m-2 s-1) | Less than 1 % (up to 4000 µmol m-2 s-1) | Less than 1 % (up to 4000 µmol m-2 s-1) | Less than 1 % (up to 4000 µmol m-2 s-1) | Less than 1 % (up to 4000 µmol m-2 s-1) | Less than 1 % (up to 4000 µmol m-2 s-1) | Less than 1 % (up to 4000 µmol m-2 s-1) | Less than 1 % (up to 4000 µmol m-2 s-1) |
| Response Time | Less than 1 ms | Less than 1 ms | Less than 1 ms | Less than 1 ms | Less than 1 ms | Software updates every second | Less than 0.6 s | - |
| Field of View | 180° | 180° | 180° | 180° | 180° | 180° | 180° | 180° |
| Spectral Range | 410 to 655 nm (wavelengths where response is greater than 50 % of maximum) | 410 to 655 nm (wavelengths where response is greater than 50 % of maximum) | 410 to 655 nm (wavelengths where response is greater than 50 % of maximum) | 410 to 655 nm (wavelengths where response is greater than 50 % of maximum) | 410 to 655 nm (wavelengths where response is greater than 50 % of maximum) | 410 to 655 nm (wavelengths where response is greater than 50 % of maximum) | 410 to 655 nm (wavelengths where response is greater than 50 % of maximum) | 410 to 655 nm (wavelengths where response is greater than 50 % of maximum) |
| Spectral Selectivity | Less than 10 % from 469 to 655 nm | Less than 10 % from 469 to 655 nm | Less than 10 % from 469 to 655 nm | Less than 10 % from 469 to 655 nm | Less than 10 % from 469 to 655 nm | Less than 10 % from 469 to 655 nm | Less than 10 % from 469 to 655 nm | Less than 10 % from 469 to 655 nm |
| Directional (Cosine) Response | ± 5 % at 75° zenith angle | ± 5 % at 75° zenith angle | ± 5 % at 75° zenith angle | ± 5 % at 75° zenith angle | ± 5 % at 75° zenith angle | ± 5 % at 75° zenith angle | ± 5 % at 75° zenith angle | ± 5 % at 75° zenith angle |
| Temperature Response | 0.06 ± 0.06 % per C | 0.06 ± 0.06 % per C | 0.06 ± 0.06 % per C | 0.06 ± 0.06 % per C | 0.06 ± 0.06 % per C | 0.06 ± 0.06 % per C | 0.06 ± 0.06 % per C | 0.06 ± 0.06 % per C |
| Operating Environment | -40 to 70 C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m | -40 to 70 C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m | -40 to 70 C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m | -40 to 70 C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m | -40 to 70 C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m | -40 to 70 C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m | -40 to 70 C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m | -40 to 70 C; 0 to 100 % relative humidity; can be submerged in water up to depths of 30 m |
| Dimensions | 24 mm diameter, 33 mm height | 30.5 mm diameter, 37 mm height | 30.5 mm diameter, 37 mm height | 30.5 mm diameter, 37 mm height | SQ-313/316/323/326: 500 mm x 15 mm x 15 mm, SQ-311/321: 700 mm x 15 mm x 15 mm | 24 mm diameter, 33 mm height | 30.5 mm diameter, 37 mm height | 30.5 mm diameter, 37 mm height |
| Mass (with 5 m of cable) | 90 g | 140 g | 140 g | 140 g | SQ-313/316/323/326: 275 g, SQ-311/321: 375g | 90 g | 140 g | 140 g |
How to Choose a Quantum Sensor
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Why do I need a PAR-Quantum Meter?
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In-depth Look at PAR-Quantum Meters
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Far-red: The Forgotten Photons
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Turning Photons Into Food
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Toward an Optimal Spectral Quality for Plant Growth and Development
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PAR Sensor Spectral Error Correction Tool
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PAR, PPF, PPFD, and PFD Explained
Photobiology Simplified with Dr Bruce Bugbee
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Applications include:
• PPFD measurements over plant canopies in outdoor environments, greenhouses, and growth chambers
• Reflected or under-canopy (transmitted) PPFD measurements in outdoor environments, greenhouses, and growth chambers
• PAR/PPFD measurements in aquatic environments, including salt water aquariums where corals are grown
If you would like to share your application of this product, please click here
Helpful Articles and Links
How to Correct for Spectral Errors of Popular Light Sources (Apogee PAR Meter LED Corrections)
Low Light Calibration Error Notice
Dana Riddle Reviews the MQ-500/510 - Dana Riddle, Advanced Aquarist
Solar, Net, and Photosynthetic Radiation - ASA Agroclimatology
Apogee MQ-510 is The First Truly Underwater PAR Meter for Hobbyists - Jake Adams, Reef Builders
Spectral Error for Apogee Instruments 500 Series Quantum Sensors/Meters White Paper
Immersion Effect Correction Factors for Apogee Quantum Sensors White Paper
USB Quantum Sensor Software Support
DLI (Daily Light Integral): Measuring Light for Plants
Comparisons in Quantum Sensor Output for Different Light Sources
Light Intensity Measurements for LEDs
Spectral Errors from Four Commercial Quantum Sensors Under LEDs and Other Electric Lights
Analysis of Spectral and Cosine Errors in Quantum Sensors
Apogee Meter Tips and Troubleshooting
PPFD to Illuminance Calculator
Converting from µmol m-2 s-1 to footcandles
Converting from µmol m-2 s-1 to Lux
Converting from µmol m-2 s-1 to mol m-2 d-1
Converting from µmol m-2 s-1 to Einsteins
Accuracy of Apogee Quantum Sensors Underwater Research Report
Comparison of Eight Quantum Sensor Models Research Report
Field of View of Apogee and SenEye Quantum Sensors Research Report
Directional Response of Apogee and Hydrofarm Quantum Meters Research Report
Apogee vs. LI-COR Quantum / PAR Sensors
The Effect of Daily Light Integral on Bedding Plant Growth and Flowering
CO2 Fluxes Over an old, Temperate Mexed Fores in Northeastern China
Biomass Production and Pigment Accumulation in Kale Grown Under Increasing Photoperiods
Photosynthetic Irradiance and Nutrition Effects on Growth of English Ivy in Subirrigation Systems
Free-Air Carbon Dioxide Enrichment of Soybean
Intermittent Light from a Rotating High-pressure Sodium Lamp Promotes Flowering of Long-day Plants
Programs are in .CR1X format and can be downloaded for use with Campbell Scientific dataloggers. Right click and select "Save target as..." or an equivalent command in your browser. They can also be viewed using Wordpad or other text viewers.
Note: In 2020 the CR1000 Campbell Scientific datalogger was discontinued. Click here to access the discontinued .CR1 format sample datalogger programs >
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