正解:C
"Semi-covert IR illumination typically operates at 850 nm. This wavelength produces a faint red glow that is somewhat visible to the human eye, making it 'semi-covert.'"
- Axis Communications Academy, Network Video Fundamentals, 2022
"850 nm is considered semi-covert, while 940 nm is fully covert."
- Axis OptimizedIR Guide
References:
Axis Communications Academy, Network Video Fundamentals, 2022 (p. 38)
Axis Web Article: OptimizedIR