Abstract: A lamp includes a main lamp body, a plurality of red light sources, a plurality of blue light sources, a plurality of white light sources, a driving board connected to the light sources to drive them to emit light, a main control circuit configured to control the driving board, and a switching circuit with a multi-position switch. The red, blue and white light sources are arranged in corresponding concentrical rings, with the red light sources in a central ring, the blue light sources in a middle ring, and the white sources in an outer ring. The multi-position switch is switched to provide input signals to the main control circuit, such that the light sources are driven to output different spectrums to meet desired plant growth spectrums.