This precision device accurately measures the amount of accumulated light that falls on any specific location on your property, giving you the ability to match a plant's light requirements with the actual light conditions measured by SunCalc. Put your plants where they want to be! Locating plants under the wrong light conditions is one of the most common reasons for plant failure. Add a soil testing meter and you have everything to guarantee plant success. SunCalc is incredibly easy to use; full instructions are included. SunCalc can be used over and over, year after year!