Sound Sensor :
Sound sensors are generally a microphone used to detect sound and return a voltage equivalent to the sound level. Using sound sensor a simple robot can be designed to navigate based on the sound receives.
Implementation of sound sensors is not easy as light sensors because it generates a very small voltage difference which will be amplified to generate measurable voltage change.
Light Sensor :
Light sensor is a transducer used for detecting light and creates a voltage difference equivalent to the light intensity fall on a light sensor.
The two main light sensors used in robots are Photovoltaic cells and Photo resistor. Other kind of light sensors like phototransistors, phototubes are rarely used.