Accurate measurement of Photosynthetically Active Radiation (PAR, 400-700 nm) in aquatic environments is accomplished using either the LI-192 Underwater Quantum Sensor or the LI-193 Spherical Quantum Sensor. Limnologists, oceanographers and biologists conducting aquatic productivity studies and vertical profiling have used these sensors extensively.

For extremely turbid conditions, radiation levels with resolution to 0.01 µmol s-1 m-2 can be measured with the LI-192 or LI-193 quantum sensors and the LI-1400 DataLogger.

Both the LI-192 and the LI-193 use computer-tailored filter glass to achieve the desired quantum response. Calibration is traceable to NIST.

Underwater or atmospheric Photosynthetic Photon Flux Density (PPFD) can be accurately measured using the LI-192SA Underwater Quantum Sensor. The LI-192SA is cosine corrected and features corrosion resistant, rugged construction for use in freshwater or saltwater and pressures up to 800 psi (5500kPa, 560 meters depth).

Absolute Calibration: ± 5% in air traceable to NIST.

Sensitivity: Typically 4 µA per 1000 µmol s-1 m-2 in water.

Linearity: Maximum deviation of 1% up to 10,000 µmol s-1 m-2.

Stability: < ± 2% change over a 1 year period.

Response Time: 10 µs.

Temperature Dependence: ± 0.15% per °C maximum.

Cosine Correction: Optimized for underwater and atmospheric use.

Azimuth: < ± 1% error over 360° at 45° elevation.

Detector: High stability silicon photovoltaic detector (blue enhanced).

Sensor Housing: Corrosion resistant metal with acrylic diffuser for both saltwater and freshwater applications. Waterproof to withstand 800 psi (5500 kPa, 560 meters).

Size: 3.18 cm Dia. x 4.62 cm H (1.25” x 1.81”).

Weight: 227 g (8 oz.).

Mounting: Three 6-32 holes are tapped into the base for use with the 2009S Lowering Frame or other mounting devices.

Cable: Requires 2222UWB Underwater Cable.

The LI-193 Underwater Spherical Quantum Sensor gives an added dimension to underwater PAR measurements as it measures photon flux from all directions. This measurement is referred to as Photosynthetic Photon Flux Fluence Rate (PPFFR) or Quantum Scalar Irradiance. This is important, for example, when studying phytoplankton, which utilize radiation from all directions for photosynthesis.

The LI-193 features a high sensitivity optical design and compact, rugged construction (3400 kPa, 350 meters depth, 3400 kPa = 493 psi).

The graph at right indicates the typical angular response of the LI-193 Spherical Quantum Sensor. The low response on the bottom of the sensor is due to light blockage by the detector housing. The error due to this low response is not significant in most cases because of the small portion of upwelling radiation compared to the total radiation.

Absolute Calibration: ± 5% in air traceable to NIST.

Sensitivity: Typically 7 µA per 1000 µmol s-1 m-2 in water.

Linearity: Maximum deviation of 1% up to 10,000 µmol s-1 m-2.

Stability: < ± 2% change over a 1 year period.

Response Time: 10 µS.

Temperature Dependence: ± 0.15% per °C maximum.

Angular Response: < ± 4% error up to ± 90° from normal axis (see Angular Response chart).

Azimuth: < ± 3% error over 360° at 90° from normal axis.

Detector: High stability silicon photovoltaic detector (blue enhanced).

Sensor Housing: Corrosion resistant metal for both saltwater and freshwater applications with an injection molded, impact resistant, acrylic diffuser. Units have been tested to 500 psi (3400 kPa, 350 meters) with no failures.

Size

Globe: 6.1 cm Dia. (2.4”).
Housing: 3.18 cm Dia. (1.25”).
Overall Height: 10.7 cm (4.2”).

Weight: 142 g (0.31 lbs.).

Mounting: Three 6-32 mounting holes are tapped into the base for use with the 2009S Lowering Frame or other mounting devices.

Cable: Requires 2222UWB Underwater Cable.