A system for measuring intensity distribution of light includes a carbon nanotube array located on a surface of a substrate, a reflector and an imaging element. The carbon nanotube array absorbs photons of a light source and radiates a visible light. The reflector is used to reflect the visible light, and the reflector is spaced from the carbon nanotube array. The carbon nanotube array is located between the reflector and the substrate. The imaging element is used to image the visible light. The imaging element is spaced from the substrate.