Apogee MQ-210X Underwater Quantum-Meter

Photosynthetic radiation is essential for the growth of the photosynthetic organisms such as corals. The wavelength range from 400 to 700 nm is PAR (Photosynthetically Active Radiation) or PPFD (Photosynthetic Photon Flux Density). Apogee quantum/PAR sensors are calibrated to measure the number of photons of light across this range.

PAR (Photosynthetically Active Radiation) is the energy source required for photosynthesis, created by photons in the wavelengths of 400 to 700 nm. The energy source, PAR, is expressed in Photosynthetic Photon Flux Density (PPFD) units, µmol m-2 s-1. PAR can be measured from both sunlight and electric light sources to ensure corals are receiving proper light or photons for optimal health. PAR requirements of coral varies greatly due to different depths and water conditions they naturally exist in. Information on specific coral PAR requirements can be found by asking a professional aquarist becoming involved in a local reef club and through articles such as Photosynthesis and Photoadaptation by Sanjay Joshi. Apogee Underwater Quantum/PAR meters and sensors accurately measure an aquariums range of PAR to give a better understanding of aquarium lighting.

Features an improved detector that provides excellent measurements under all light sources, including LEDs, right out of the box. The full-spectrum quantum sensor has a spectral range of 389 to 692 nm ± 5 nm. The sensor is available attached to a hand-held meter that provides a digital readout (MQ-510), with USB communication and custom software (SQ-520), and in multiple analog outputs to be used with a datalogger or voltmeter.

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. The original quantum sensor has a spectral range of 410 to 655 nm. The sensor is available attached to a hand-held meter that provides a digital readout (MQ-210) and in multiple analog outputs to be used with a datalogger or voltmeter.

All Apogee Underwater Quantum Meters and Sensors models (MQ-210 and -510, and SQ-420 and -520) automatically correct for the immersion effect or have an immersion setting, allowing the user to make excellent underwater measurements right out of the box. Sensors feature a waterproof sensor head that is potted solid for a complete seal and to ensure it has no hollow cavities for water to penetrate and cause measurement errors.

Quantum sensors are increasingly used to measure photosynthetic photon flux density (PPFD, units of µmol m-2 s-1) underwater, which is important for biological, chemical, and physical processes in natural waters and in aquariums. When a quantum sensor that was calibrated in air is used to make underwater measurements, the sensor reads low.

This phenomenon is called the immersion effect and happens because the refractive index of water (1.33) is greater than air (1.00). The higher refractive index of water causes more light to be backscattered (or reflected) out of the sensor in water than in air (Smith, 1969; Tyler and Smith, 1970). As more light is reflected, less light is transmitted through the diffuser to the detector, which causes the sensor to read low. When this effect is not corrected for, underwater measurements are only relative, which makes it difficult to compare light in different environments.

The Apogee Full-Spectrum Quantum Sensor (model SQ-500) is more spectrally accurate than the Original Quantum Sensor (model SQ-120-SS), but the unique optics (mainly the shape) cause the immersion effect to be larger for the new sensor. Underwater PAR measurements collected using a full-spectrum sensor can be corrected by multiplying by 1.32; measurements collected using an original Apogee sensor should be multiplied by 1.08*.

The MQ-210 and MQ-510 Underwater Quantum Meters already apply the immersion effect correction factor to the meter readings through the meter firmware. Additionally, the SQ-420 and SQ-520 have an "Immersion Setting" that applies the immersion effect correction factor to the sensor readings through the ApogeeConnect Software. These sensors do not need post-measurement corrections applied to their measurements.

The MQ-210 and -510 meters record up to 99 manual measurements. In logging mode the meter will make a measurement every 30 seconds. Every 30 minutes the meter will average the sixty, 30-second measurements and record the averaged value. The meter can store up to 99 averages. The SQ-420 and -520 USB sensors have internal memory capable of storing 10,000 user-specified periodic measurements that can be downloaded to a computer, however, the integrated daily total can only be viewed by downloading the data to a computer. Downloading data to a computer requires the AC-100 communication cable (a standard USB cable will not work) and Apogee-AMS-Software.

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.

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.