A phototransistor with maximum response in the infrared region of the spectrum at around 940nm. This is near to the visible region of the spectrum. The phototransistor is mounted on the end of a fibreglass wand, fitted with a 250mm lead and two 4mm connectors. When connected to a suitable voltmeter (e.g. IPC-1904-M 2V d.c. voltmeter) the probe will produce a qualitative reading proportional to the amount of infrared radiation incident on it's sensitive face. Supplied with instructions.