The remote control contains an infra-red LED which emits a coded pulse train in a single wavelength to a spectrally matched receiver. Since LEDs are available at wavelengths throughout the visible spectrum, and into the ultra-violet, why is infra-red used exclusively for remote control? I remember once having a TV that had an ultrasonic control so it's clearly not the wavelength that's important, and it would be useful if the controller emitted, say, yellow light as you could see it was working.....
