The information-hungry world of the 21st century will be fed not by electrical signals, but by pulses of invisible laser light flying along fibres of glass.

What is the revolution in communications that has ousted electricity in favour of light?

With crashing motorbikes, stretching trains and a semiconductor laser the size of a department store, Horizon investigates the mysterious world of light technology and, at the frontiers, finds plans for computers that will process information with light.

What all this might mean for people 25 years from now is seen in the touching tale of Alan and Sarah.

Narrator Tim Pigott-Smith

(Ceefax Subtitles)