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Apogee Instruments' quantum sensors provide accurate and cost-effective measurement of photosynthetically active radiation (PAR) from all light sources used to grow plants and corals.


Accurate, Stable Measurements
Sensors are cosine-corrected to maintain their accuracy when radiation comes from low zenith angles. The sensors measure PPFD with a cosine response accurate within ± 5 % at 75° zenith angle. Long-term non-stability determined from multiple replicate quantum sensors in accelerated aging test and field conditions is less than 2 % per year.


Spectral Response
The full-spectrum quantum sensor has a spectral range of 389 to 692 nm ± 5 nm. The improved spectral response increases the accuracy of LED measurements. The spectral responses can be seen in the graph below. 


To ensure accuracy each sensor is carefully calibrated in controlled conditions and traceable to NIST reference standards. The full-spectrum sensors are pre-calibrated for all light sources.


Rugged, Self-cleaning Housing
Patented domed shaped sensor head (diffuser and body) facilitate runoff of dew and rain to keep the sensor clean and minimize errors caused by dust blocking the radiation path. Sensors are housed in a rugged anodized aluminum body and electronics are fully potted.

Typical Applications
PPFD measurements over plant canopies in outdoor environments, greenhouses, and growth chambers, and reflected or under canopy (transmitted) PPFD measurements in the same environments. Quantum sensors are also used to measure PPFD in aquatic environments, including salt water aquariums where corals are grown.


Ideal for Measurements in Air
and Underwater

Apogee quantum sensor are calibrated to make absolute PPFD measurements in air. The waterproof sensors can be used to make absolute PPFD measurements underwater by applying an immersion effect correction factor, the SQ-420, SQ-520, MQ-210, and MQ-510 already apply the correction factor. For details on making underwater measurements, please refer to Underwater PAR Measurements.

Output Options
Available in a 0 to 40 mV analog output option. Additionally, a digital "smart" sensor that uses USB communication and custom software to interface directly to a computer is available. Sensors are also available attached to a hand-held meter with digital readout.

The AL-120 Solar Mounting Bracket with Leveling Plate facilitates mounting the sensor to a mast or pipe. The AL-100 Solar Sensor Leveling Plate is designed to level the sensor while sitting on a flat surface or mounting to a surface.


Warranty and Support
All Apogee products are backed by an industry-leading four year warranty and outstanding customer support.



Need help choosing a sensor?

  Technical Information
Technical Information
Find knowledge base articles, manuals, FAQs, technical support, and more.
+ What type of Quantum Sensor do I need?
Apogee Instruments produces two types of quantum sensors.

The Original Quantum Sensor (SQ-100, SQ-200, SQ-300, and SQ-400 Series) have a spectral range of 410 to 655 nm. The Original Quantum Sensor works great for most single light, non-LED, and sun applications.

The Full-spectrum Quantum Senor (SQ-500 Series) has a spectral range of 389 to 692 ± 5 nm. The Full-spectrum quantum sensor is the best option for LED and multiple light applications.

Once sensor type is determined, you will need to decide what output is needed to determine the sensor model number. This is usually dependent on the type of controller/logger you have.

+ Which Full-spectrum Quantum Sensor model do I need?
All Full-spectrum Quantum Sensors (SQ-500 series) use the same detector. The model number you need depends on which output is compatible with your datalogger. Model numbers are listed below with their output:
SQ-500 0 to 40 mV 0 to 4000 µmol m-2 s-1
SQ-520 USB/software 0 to 4000 µmol m-2 s-1
MQ-500 Sensor attached to a handheld meter with digital readout 0 to 4000 µmol m-2 s-1

*The above ranges are standard and built to stock. If you need a larger range than what is listed please contact technical support for a quote on your specific requirement.

+ Which Quantum Sensor should I purchase for my Greenhouse?
You should purchase the quantum sensor that matches your greenhouse light source the closest. We recommend an electric light calibrated sensor to measure supplemental electric lighting, a sunlight calibrated sensor to measure daylight PAR, and the SQ-500 series sensor for LED lights.
+ What Quantum Sensor should I purchase for my Aquarium?
You should purchase the quantum sensor that matches your aquarium light source the closest. We recommend the MQ-210 or SQ-420 for supplemental electric lighting and sunlight. We recommend the MQ-510 or SQ-520 for LED lights. Apogee does offer meters and sensors, models (MQ-210, MQ-510, and SQ-520), that are ready out of the box for underwater measurements. These underwater meters and sensors are preprogrammed with the immersion effect correction factor, so no post-measurement corrections need to be made. All other Apogee quantum sensors and meters need to have their respective immersion effect correction factor multiplied to their reading. For more information on underwater PAR measurements click here.
+ Are Apogee Quantum Meters waterproof?
The handheld meter is not waterproof, only the sensor and cable are waterproof. If Apogee quantum sensors are used underwater, please refer to Underwater PAR Measurements or the Underwater Measurements and Immersion Effect section of your owner's manual.
+ Do I need to order a sensor to go with my meter?
No. All Apogee meters (MO, MP, MQ, and MU series) either have sensors built into the meter or attached via two meters of cable. If you order a sensor only (SI, SO, SP, SQ, and SU series) you will need to have your own datalogger (or, depending on the sensor, a voltmeter) to collect information form the sensor.
+ What is the difference between the MQ-500 and MQ-510?
The only difference between the MQ-500 and MQ-510 is the MQ-510 has the immersion effect correction factor already applied to the meter readings so there is no need for post-measurement corrections for underwater measurements.

spec sheets
Specification Sheets




Case Studies

PAR Measurements Characterize Tree Coverages

PAR Measurements Characterize Tree Coverages
Using line quantum meter to study the percent of PAR (under canopy/open sky) and its relation to survival and initial growth of native forest species.
Read More >


Line Quantum in Greenhouse

Controlling Flowering of Orchids in Greenhouse
Line quantum sensor used to measure PPFD and daily light integral, while experimenting with temperature to control flowering.
Read More >

View all Case Studies >



How to Choose a Quantum Sensor

Why do I need a PAR-Quantum Meter?

In-depth Look at PAR-Quantum Meters

Lecture 4-PAR

Apogee Instruments Meter User Guide

How to Use the AL-120 Leveling System