This Sun System 748200 PAR meter features an integrated sensor which measures photosynthetic active radiation (PAR), the spectral range of solar radiation that photosynthetic organisms are able to use in the process of photosynthesis. Since the meter is calibrated for both electric light and sunlight, the meter can be used inside with Sun System grow lights or outside with natural sunlight. This PAR meter is compact in size, while the four buttons make it easy to use. The meter has two modes, one for manual measurements and one for automatic measurements, and up to 99 measurements can be recorded in each mode. CR2032 battery included.