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 almost universally quantified as photosynthetic photon flux density (PPFD) 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). However, ultraviolet and far red photons outside the defined PAR range of 400-700 nm can also contribute to photosynthesis and influence plant responses (e.g., flowering).
Sensors that measure PPFD are often called quantum sensors due to the quantized nature of radiation. A quantum refers 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. Sensors that function like traditional quantum sensors, but measure a wider range of wavelengths can be thought of as an ‘extended range’ quantum sensor.
Typical applications of traditional quantum sensors include incoming PPFD measurement over plant canopies in outdoor environments or in greenhouses and growth chambers, and reflected or under-canopy (transmitted) PPFD measurement in the same environments. Apogee's new 400-750 nm extended photosynthetically active radiation (ePAR) sensor is designed for making total photon intensity measurements of wider ranges than traditional PAR sensors that measure 400-700 nm.
| SQ-610-SS | SQ-612-SS | SQ-614-SS | SQ-615-SS | SQ-616 | SQ-617-SS | SQ-618-SS | |
|---|---|---|---|---|---|---|---|
| Power Supply | Self-powered | 5 to 24 V DC | 12 to 24 V DC | 5.5 to 24 V DC | 5 V USB power source | 5.5 to 24 V DC | 5.5 to 24 V DC |
| Current Draw | - | at 12 V is 57 µA | Maximum of 20 mA | at 12 V is 57 µA | 61 mA when logging | 1.4 mA (quiescent), 1.8 mA (active) | RS-232 37 mA; RS-485 quiescent 37 mA, active 42 mA |
| Sensitivity | 0.01 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 | - | - | - |
| Output Type | 0 to 40 mV | 0 to 2.5 V | 4 to 20 mA | 0 to 5 V | USB | SDI-12 | Modbus |
| Resolution | - | - | - | - | 0.1 µmol m-2 s-1 | - | - |
| Calibration Factor | 100 µmol m-2 s-1 per mV | 1.6 µmol m-2 s-1 per mV | 250 µmol m-2 s-1 per mA | 0.8 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 % |
| Measurement Range | 0 to 4000 µmol m-2 s-1 | 0 to 4000 µmol m-2 s-1 | 0 to 4000 µmol m-2 s-1 | 0 to 4000 µmol m-2 s-1 | 0 to 4000 µmol m-2 s-1 | 0 to 4000 µmol m-2 s-1 | 0 to 4000 µmol m-2 s-1 |
| 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 0.5 % |
| Long-term Drift 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) |
| Response Time | 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° |
| Spectral Range | 394 to 747 nm ± 5 nm (wavelengths where response is greater than 50 % of maximum) | 394 to 747 nm ± 5 nm (wavelengths where response is greater than 50 % of maximum) | 394 to 747 nm ± 5 nm (wavelengths where response is greater than 50 % of maximum) | 394 to 747 nm ± 5 nm (wavelengths where response is greater than 50 % of maximum) | 394 to 747 nm ± 5 nm (wavelengths where response is greater than 50 % of maximum) | 394 to 747 nm ± 5 nm (wavelengths where response is greater than 50 % of maximum) | 394 to 747 nm ± 5 nm (wavelengths where response is greater than 50 % of maximum) |
| Directional (Cosine) Response | ± 2 % at 45°; ± 5 % at 75° zenith angle | ± 2 % at 45°; ± 5 % at 75° zenith angle | ± 2 % at 45°; ± 5 % at 75° zenith angle | ± 2 % at 45°; ± 5 % at 75° zenith angle | ± 2 % at 45°; ± 5 % at 75° zenith angle | ± 2 % at 45°; ± 5 % at 75° zenith angle | ± 2 % at 45°; ± 5 % at 75° zenith angle |
| Azimuth Error | 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 0.5 % |
| Tilt Error | 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 0.5 % |
| Temperature Response | -0.11 ± 0.04 % per C | -0.11 ± 0.04 % per C | -0.11 ± 0.04 % per C | -0.11 ± 0.04 % per C | -0.11 ± 0.04 % per C | -0.11 ± 0.04 % per C | -0.11 ± 0.04 % per C |
| Uncertainty in Daily Total | Less than 5 % | Less than 5 % | Less than 5 % | Less than 5 % | Less than 5 % | Less than 5 % | Less than 5 % |
| Housing | Anodized aluminum body with acrylic diffuser | Anodized aluminum body with acrylic diffuser | Anodized aluminum body with acrylic diffuser | Anodized aluminum body with acrylic diffuser | Anodized aluminum body with acrylic diffuser | Anodized aluminum body with acrylic diffuser | Anodized aluminum body with acrylic diffuser |
| IP Rating | IP68 | IP68 | IP68 | IP68 | IP68 | IP68 | IP68 |
| 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 |
| Dimensions | 30.5 mm diameter, 37 mm height | 30.5 mm diameter, 37 mm height | 30.5 mm diameter, 37 mm height | 30.5 mm diameter, 37 mm height | 30.5 mm diameter, 37 mm height | 30.5 mm diameter, 37 mm height | 30.5 mm diameter, 37 mm height |
| Mass (with 5 m of cable) | 140 g | 140 g | 140 g | 140 g | 140 g | 140 g | 140 g |
| Warranty | 4 years against defects in materials and workmanship | 4 years against defects in materials and workmanship | 4 years against defects in materials and workmanship | 4 years against defects in materials and workmanship | 4 years against defects in materials and workmanship | 4 years against defects in materials and workmanship | 4 years against defects in materials and workmanship |
Is PAR really 400-700 nm? The McCree Curve Revisited with Evidence ePAR should be the New Standard
ePAR Explained with Dr. Bruce Bugbee
Predicting Stem Elongation and Leaf Expansion: Percent far-red is a better predictor than PPE
If you can't access the video via Youtube, click here.
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
If you can't access the video via Youtube, click here.
PAR, PPF, PPFD, and PFD Explained
Photobiology Simplified with Dr Bruce Bugbee
If you can't access the video via Youtube, click here.
Meter User Guide 2023
Applications include:
• Total ePAR intensity measurements over plant canopies in all growing environments
• Monitor and adjust grow lights
• Research plant morphogenic activity
• Photobiology studies
If you would like to share your application of this product, please click here
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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