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Spectral band and the IR-cut filter

Silicon sees infrared. Colour cameras have to pretend they do not.
​ 12 September 2026 by

Silicon sees further into infrared than your eye. A colour camera therefore needs a filter that throws most of that IR away, or daylight foliage goes purple and black clothes go grey. A mono night camera often wants the opposite: take the IR, add a lamp at 850 or 940 nm, and keep the photons. Spectral band and IR-cut on a Camemaker lens page are that decision.

Garden in natural colour beside the same garden with a purple infrared colour shift
Left is a cut that matches the eye. Right is silicon being honest about NIR. Only one of them is a colour product.

In one sentence. IR-cut is for colour that should look like daylight. No cut (or a switchable cut) is for night and mono. Do not mix them and blame the sensor.

The usual mistakes

  • Bayer sensor, no IR-cut: pretty demo indoors, sickly outdoor.
  • Mono sensor, strong IR-cut: you paid for sensitivity and then filtered it out.
  • Day-night security: needs a moving cut or a dual filter. A glued cut is a day camera.
  • 850 versus 940 nm lamps: 940 is dimmer to the eye and often to the sensor. Check QE at that wavelength.

How to pair it

Read CFA on the sensor and IR-cut plus spectral band on the lens as one sentence. RGB plus IR-cut is a colour camera. Mono plus no cut is a night camera. RGB-IR is the awkward middle and only works if the ISP knows which wells are which.

TTL, optical BFL, and mechanical BFL
The glass can screw in and still sit in the wrong place.