An electronic device may be operated in ambient light. The electronic device may have a color ambient light sensor that is configured to produce color ambient light sensor data based on the ambient light. The electronic device may also have a flicker sensor that has a faster response time than the color ambient light sensor and that is used in detecting dynamic changes in the ambient light. Control circuitry in the electronic device may analyze flicker sensor data to identify the number of light sources producing the ambient light. The control circuitry may apply a frequency transform to the flicker sensor data or make measurements with the flicker sensor in multiple directions. Based on this information, the control circuitry may identify the number of light sources and may use this information in retrieving an ambient light spectrum associated with the ambient light using the color ambient light sensor data.