Spherical Underwater Quantum Sensor

The LI-193 Spherical Quantum Sensor measures PAR in air or underwater from all directions at depths up to 350 meters. This sensor is useful for studies of phytoplankton, which uses radiation from all directions. The measurement is referred to as Photosynthetic Photon Flux Fluence Rate (PPFFR) or Quantum Scalar Irradiance.

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Why choose the LI-193?

  • Designed for immersion
  • Measures PAR from all directions
  • Ideal for oceanography, limnology, turbidity, and vertical profiling
LI-193 Spherical Underwater Quantum Sensor

How does it work?

The LI-193 uses a diffusive sphere to direct light through glass optical filters to the silicon photodiode. The filters create uniform sensitivity to light between 400 and 700 nm, which closely corresponds to light used by most terrestrial and aquatic plants and algae. The angular response of a typical LI-193 is slightly lower in the direction of the cable connection. When mounted, the low response is usually not significant due to the small proportion of upwelling radiation compared to the total.

Angular response graph of the LI-193 Spherical Quantum Sensor
Typical angular response of the LI-193

Cables and Accessories

LI-193 cables are available in lengths from 3 meters to 100 meters.

We recommend the 2009S Lowering Frame to lower the sensor into water.

LI-193 Specifications

  • Absolute Calibration: ± 5% in air traceable to NIST
  • Sensitivity: Typically 7 μA per 1,000 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: Acrylic diffuser.
  • Angular Response: < ± 4% error up to < ± 90° from normal axis.
  • 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 3,400 kPa (500 psi), 350 meters with no failures.
  • Dimensions
  • 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 lb.).
  • 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.
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