All types of Color Sensors comes under this category.
Color Sensor Module GY-31
GY-31 Color Sensor Module is made using IC TCS3200, a programmable color light to frequency converter. It has configurable silicon photodiodes and a current to frequency converter in a single monlithic CMOS Integrated Circuit. Its output is square wave having 50% duty cycle with frequency directly proportional to irradiance (light intensity). This module can be directly interfaced with Microcontrollers, Arduino Boards, Raspberry Pi etc.