1. Collision detection and ground detection
2. Passive Sensors
3. Photocell (LDR): Street light trigger
4. Used in potential divider configuration
5. Light (photons) transfer energy to bound electrons
6. IR, visible, UV
7. Active sensors
8. Emitter: Infrared LED-Detector, Photo-diode (faster) or photo-transistor (sensitive)
9. Used for proximity sensing
10. Responsiveness to a wide range of frequencies