When considering how to calculate the average light in a greenhouse over the course of a year, one typically relies on the concept of Daily Light Integral (DLI). This metric indicates the amount of light received on average each month. DLI data for various regions are readily available online, offering monthly averages over time. By accessing these resources, greenhouse owners can observe fluctuations in light levels, particularly noting the decreased illumination during winter months. From these observations, it becomes feasible to determine the extent of supplemental lighting required to compensate for reduced natural light and maintain the typical yearly average.