hi Ben,benpaddlejones said:An IR emitter is simply an LED that transits light at a spectrum that our eyes can not detect (usually arround 950nm).
An IR Sensor simply detects light arround 950nm.
Most mobile phones have an IR sensitive lense. Get your TV remote (the LED at the front is an IR LED) and push a few buttons while looking at the IR LED through your mobile phone camera and you will see it flash.
n.b ultraviolet is arround 350nm and white light arround 150nm