A spectrally tunable light source is presented. The light source can be used to create a wide variety of spectral power distribution. The design of a spectrally tunable light source system includes thousands of high power light emitted diodes (LEDs) across the whole visible spectral region. Besides being used to calibrate optical remote sensors, the spectrally tunable light source can be used for the detection calibration of photometers and radiometers. By using this system to simulate different lighting conditions, the material property and object reflectivity can be assessed. In addition, this system can also be used in displays.