## Common ground
All options are types of photodetectors that convert light into electrical signals.
## Options at a glance
**8536.50 – Motion detector (PIR)**
- **Defining trait:** Detects infrared radiation emitted by moving warm bodies (like humans), not ambient light.
- **Typical examples:** PIR sensors in security alarms, automatic lights.
- **Best fit when:** The device is used for motion detection in security or automation systems.
**9027.50 – Optical radiation detector (UV/visible/IR)**
- **Defining trait:** Detects a broad range of optical radiation (ultraviolet, visible, infrared) for sensing or measurement.
- **Typical examples:** Light meters, spectrometers, environmental sensors.
- **Best fit when:** The device measures light intensity across UV, visible, or IR wavelengths.
**9027.89 – Near-infrared detector**
- **Defining trait:** Specialized for near-infrared (NIR) wavelengths, often used in communication or imaging.
- **Typical examples:** Fiber optic receivers, remote controls, NIR cameras.
- **Best fit when:** The device is designed specifically for near-infrared light detection.
## Key differences
| Feature | 8536.50 (PIR) | 9027.50 (Optical) | 9027.89 (NIR) |
|-----------------------|---------------------|------------------------|------------------------|
| Primary radiation | Thermal IR (body heat) | UV, visible, IR | Near-infrared only |
| Main function | Motion detection | Light sensing/measurement | Signal reception |
| Application focus | Security systems | Scientific/industrial | Telecom/imaging |
## How to choose
- Does it detect movement via body heat? → 8536.50
- Does it sense UV, visible, or broad IR light? → 9027.50
- Is it designed specifically for near-infrared wavelengths? → 9027.89
## Overlaps & pitfalls
- A PIR sensor (8536.50) may use an infrared detector, but its function is motion-based, not general light sensing.
- An NIR detector (9027.89) falls under the broader category of optical radiation detectors (9027.50), so overlap exists.
- If a device detects both motion and light, prioritize based on **main function**: security activation → 8536.50; light measurement → 9027.50; NIR-specific use → 9027.89.
- No clear priority rule given; user must decide based on the product’s primary purpose