The present invention is an accumulated light meter that generates data concerning the quantity of photosynthetically active radiation available over a measured period of time. The device can calculate a daily light integral (DLI) that corresponds to the amount of light required by certain plants in order to optimize photosynthesis. The device also possesses the ability to filter out the effect that wavelengths of unproductive light have on the calculated values since not all light is conducive to photosynthesis and different species of plants can utilize different wavelengths of light in dissimilar ways.