There was a small rubber sucker attachment that you could stick to a TV screen, with the light pen attached. The BBC (tv station) had a programme (probably MicroLive) that would overlay a flashing block on a small section of the screen. The light pen would read that flashing and you'd have a small program.
I recall seeing a torrent of the full series a while back - I'd like to think that it's probably still possible to decode the programs even today. :)
4 Computer Buffs also transmitted some software as audio, usually over teletext pages or the test card, while the channel was off air - again, see here:
One of the BBC programmes - either 'The Computer Programme' or 'Making The Most Of The Micro' transmitted a BBC Micro program as audio, too, but they intentionally kept it very short so as not to offend viewers who didn't like the noise.
That said, they lengthened the broadcast as a result of transmitting the program at 300 baud - they did tell everyone at home to make sure they typed *TAPE 3 (i.e. to crank the loading speed down to 300 baud rather than the Beeb's normal 1200 baud), presumably to strengthen the chances of some usable data actually making it through. :)
There was a small rubber sucker attachment that you could stick to a TV screen, with the light pen attached. The BBC (tv station) had a programme (probably MicroLive) that would overlay a flashing block on a small section of the screen. The light pen would read that flashing and you'd have a small program.
Here's someone talking about it:
http://forums.theregister.co.uk/forum/1/2014/02/18/ian_mcnau...
The BBC (and Sinclair, and possibly Amstrad) did a lot to make computing accessible.
http://www.bbc.co.uk/news/technology-15969065