Skye SKP 200 Professional Laboratory Grade Quantum PAR Meter with waterproof and submersible to 4 meters sensor (SKP 215). Has case and extra 9 volt battery. Measures PAR Spectrum in units of umol m2 sl (number or quanta of photons). Used in aquarium environments (Reef Tanks etc), plant and crop research, and commercial horticulture applications. PAR is short for Photosynthetically Active Radiation. This part of the solar spectrum (400-700 nm) is used by plants for photosynthesis and sugar production.