When accuracy is important, you can count on the Extech light meter to deliver. This unit reads both Lux (0-50,000) and Foot-candle (0-5,000) +/- 5%. Instructions include the correction factor for both sodium and metal halide. Operates on one 9 Volt battery (included). Maximize your growth by being sure of adequate lighting. Replace your bulbs in a timely manner by monitoring your bulb’s output.