🔍 Key Concepts

• Optoisolator vs optointerrupter – how light is used between LED and photodiode • Difference between devices that transmit through a gap versus devices that detect reflections or ambient light • Typical construction of a light sensor inside a light‑tight enclosure

💭 Think About

• Is the LED’s light meant to be blocked by an object or to shine continuously onto the photodiode? How does that affect the name of the device? • Which of these choices describes a pair of components working together (LED + detector), versus a display device or a single sensor? • Why would the enclosure need to be light‑tight? What does that tell you about whether the device should ignore outside light or rely on it?

✅ Before You Answer

• Identify which options are two‑part opto devices (emitter + detector) and which are not • Think about whether the device is used mainly for displaying digits or for sensing/isolating signals • Confirm which term is used for a device where an LED shines at a detector inside a shielded housing, often with a slot or gap for objects to pass through