The Milwaukee Portable Lux Light Meter is a quick and simple way to determine and optimize light intensity in your aquarium. It features a waterproof sensor that accurately measures how much light your corals and other inhabitants are receiving. It ranges between 0.000 to 50000 Lux with a ±6% of reading ±1 digit accuracy. Includes a 9V battery. Measures 3″W x 5 1/2″H.