Described are a method and a photodetector system for determining a wavelength of light. A current generated in a photodetector in response to incident light is determined. The incident light is terminated and a decay current generated by the photodetector is determined. The wavelength of the light is determined according to the current, the decay current and a predetermined correspondence between the current and decay current as a function of wavelength and time. In one embodiment, the decay current is compared to reference decay currents to determine a matched reference decay current and the wavelength of the light is determined according to a wavelength associated with the matched reference decay current.