What is a common application for photodetectors?

Photodetectors are primarily used to convert light into a measurable signal, which is essential in various applications such as telecommunications, imaging systems, and environmental monitoring. When light photons hit the photodetector material, they generate electrical signals based on the intensity of the light. This process is crucial in technologies like fiber optics, where light signals need to be converted into electronic signals for processing and analysis.

In contrast, measuring speed, detecting sound waves, and storing data do not directly involve the primary function of photodetectors. Measuring speed typically involves different sensors and equipment, while detecting sound waves pertains to microphones or acoustic sensors. Storing data is associated with storage devices and memory systems, not with the detection and conversion of light. Thus, the conversion of light into a signal remains the core application of photodetectors, validating the choice as the correct answer.