A modular LED system is provided that includes a frame having a plurality of light emitting diodes (LEDs) of at least two different colors for generating light within a color spectrum. The LEDs are mounted on or adjacent to a plate equipped with cooling medium for cooling the LEDs. The system includes a processor for controlling an amount of electrical current supplied to the LEDs to determine a color of light generated by the LEDs, and a flat translucent member having translucent lenses for decreasing or increasing the diffusion angle for light emitted from each LED. The system is suitable for illuminating plants to supplement natural light without substantially interfering with the amount of natural light due to its narrow width. The system delivers uniform illumination and reduces energy and maintenance costs. The system may be installed in a commercial greenhouse.
