Combining Sunlight & Grow Lights: Supplemental Greenhouse Lighting by Kent Gruetzmacher Indoor and outdoor growing are no longer distinct schools of thought. Greenhouse cultivators have combined the practices to create a new, more cost-effective method that uses both sunlight and grow lights to power crop production. 44 Maximum Yield O nce considered two distinct schools of thought in horticulture, the line between indoor and outdoor cultivation is being blurred. Highly sophisticated, year-round greenhouses are at the forefront of this fusion movement as they utilize the best practices of both methodologies in a creative give and take. These operations utilize the sun’s energy to power essential plant functions while implementing indoor growing technologies like light sensors, blackout tarp systems, dehumidifiers, and industrial heaters to mimic indoor environmental controls in outdoor settings. Perhaps the most vital technological application in these modern-day greenhouses is that of supplemental lighting. In indoor gardening, lighting is one of the most important factors dictating the outcome of a harvest. However, it is also one of the costliest elements of an operation, with an overhead of at least $400 per unit for 1,000W double-ended high pressure sodium (HPS) lights and $800 per unit for comparable light emitting diodes (LEDs). Taken to a commercial scale, this overhead can prove quite intimidating as it is solely up to these artificial light sources to feed every square inch of a massive garden canopy. Then there is the astronomical cost of running the lights in these large-scale set-ups. Some 10,000-square-foot warehouse grows have reported power bills to the tune of $12,000 monthly.