The invention includes methods and systems of optimizing plant growth where the quantity and quality of ambient light received by a plant is measured, the difference between the measured ambient light and an optimized target spectral irradiance is determined, and a light source is adjusted to provide supplemental light in a quantity and quality to achieve the target spectral irradiance. A light source may include a plurality of LEDs, configured to have a combined output which is adjustable for frequency and intensity and a radiometer for measuring ambient light. The light source further includes a control system which receives the output of the radiometer, determines the difference between the ambient spectral irradiance and a target spectral irradiance, and causes the plurality of LEDs to emit supplemental light substantially equal to the difference. A lighting system may include separate light sources and radiometers for different zones, allowing for separate and customized control for each zone.
