Education · · 3 min
Why iris cameras use near-infrared light
Near-infrared imaging reveals iris texture independent of eye color and ambient lighting, which is why it underpins virtually every operational iris system.
Look at an iris scanner and you won’t see a flash — the light it uses is invisible. Virtually all deployed iris systems image the eye in the near-infrared (NIR) band, roughly 700–900 nm.
The reason is physics. Melanin, the pigment that makes dark eyes dark, is nearly transparent in the near-infrared. Under NIR the iris’ fine texture becomes readable regardless of eye color — so the same algorithm works on brown, blue and very dark eyes alike. It also sidesteps the ambient lighting and glare that plague visible-light capture.
Wavelength still matters. NIST’s multispectral study found matching accuracy can vary by more than an order of magnitude across the NIR band for some algorithms, with best performance generally around 800–910 nm (an estimated optimum near 850 nm). International standards specify the NIR band for interoperable iris imagery.
This is why iris scanners are engineered around specific NIR illuminators and sensors — and why near-infrared, not the visible photo you’d take with a phone, is the foundation of operational iris recognition.