This invention discloses an illumination method and an illumination control method. An embodiment of the illumination system includes two light detection modules for detecting a light produced by a light emitting diode and an ambient light, calculating a reference spectral distribution based on a detection result of the ambient light, comparing the detection result of the light emitting diode with the reference spectral distribution, and driving the illumination module to emit a light matching with the reference spectral distribution based on a comparison result. Another embodiment of the illumination system includes a light detection module for periodically switching the light emitting diode to emit light and stop emitting light. When the light emitting diode stops an illumination period, the light detection module detects an ambient light, and when the light emitting diode continues an illumination period, the light detection module detects a light produced by the light emitting diode.