Semi-covert IR-light has a wavelength of

"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