Tiny handheld delivers accurate solar power readings

The handheld M140 mini solar power meter measures solar irradiance in user-selectable units of W/m² or BTU/(ft² *hr). It measures various light sources, including all visible light,  displays overload display OL,  and provides manual on/off or auto shutoff after 15 min. In sunlight, its typical accuracy is within ±10 W/m² [±3 BTU/(ft² *hr)] or ±5%, whichever is greater. The meter displays 3¾ digits with a maximum reading of 3999.

The M140 mini solar power meter has a sample rate of about 0.25 s, runs for 50 hours from its battery, and measures 134 x 48 x 27 mm. It's priced at $115.