Any electromagnetic wave can be changed or 'modulated' in order to carry information. In the case of radio waves, if we change the amplitude of the carrier wave we get amplitude modulation (or AM radio) and if the modulate the frequency, we get FM radio. This science kit demonstrates that you can modulate light (which is also part of the electromagnetic spectrum of course) in order to carry a signal.
The torch or flashlight is the 'transmitter' and has a cable connected to it with a 3.5mm jack at the end. You need to plug this into the headphone socket of any sound source, such as a mobile phone or MP3 player. Although it is not visible to the eye, the amplitude of the light beam is now being 'modulated' by whatever you are using as your sound source.
Switch on the 'receiver' and shine the light onto the solar panel on the front. The receiver will decode the modulated light beam, and play the audio signal out of the integrated loudspeaker.
The kit contains a leaflet and instructions for 10 experiments that you can carry out (some of the experiments will require additional equipment).
The torch will need 3 x AAA batteries, the receiver needs 2 x AA batteries. You will also need to provide a sound source, such as an MP3 player or a mobile phone.