Photodetector shows that the electromagnetic spectrum extends on either side of the visible spectrum. The detector area is only 1mm dia. so that it can be passed through the visible spectrum produced by a projector and prism. The output is monitored on a multimeter and gives measurable readings from 300nm to 1000nm demonstrating the presence of invisible UV and IR. Requires 9V battery and multimeter with 200mV scale or similar (not included).