A shower of meteorites produces a glow that blinds anyone that looks at it. As it was such a beautiful sight, most people were watching, and as a consequence, 99% of the population go blind. In the original novel, this chaos results in the escape of some Triffids: experimental plants that are capable of moving themselves around and attacking people. In the film version, however, the Triffids are not experimental plants. Instead they are space aliens whose spores have arrived in an earlier meteor shower.
The link to the full film is below – (Public Domain)