The Apogee Instruments' DLI-600 is an elegant, simple-to-use device for spot checking photosynthetically active radiation (PAR) beyond the traditionally 400–700 nm range. The DLI-600 measures the newly defined 400-750 nm ePAR radiation range, which has been shown to have extended photosynthetically active properties. In addition to measuring ePAR, the DLI-600 meter calculates daily light integral (DLI) and photoperiod. DLI refers to the total amount of PAR or ePAR incident on a plane in a 24-hour period, expressed in units of moles per square meter per day (mol m-2 d-1). Photoperiod is the total amount of time in which PAR or ePAR is incident on a plane during a 24-hour period and is expressed in units of hours (h). ePAR, DLI, and photoperiod influence plant growth and development, and they are often measured in greenhouses and growth chambers to aid in light management and decision making.