Because his eyes can perceive all visible as well as invisible waves and especially the infra-red rays.

Its auto-focus mechanism not only calculates distances, but projects infra-red rays harmlessly into your retina.

But a red light, fed by chemicals - a light that produced infra-red rays as well - could have been easily distinguished.

I think many of the infra-red rays bounce off the white paint, much like visible light does.

There could be movement detectors, infra-red rays, a microwave Doppler device.

In the active method an invisible infra-red ray is emitted.

As it began to run a little hot the heat waves streamed out - visible to him as infra-red rays.

All electro-magnetic frequencies down to the long wavelengths of infra-red rays were blocked out.

The pit organs of snakes can gather these infra-red rays to form a crude heat picture.

There are infra-red rays and other things coming out of that blue-light phenomenon.