Re: IrDA
> But if we all have to buy new LiFi light fittings (ant bets?) not so good.
True, but for new buildings or major refurbishments this is less of an issue.
> Does than mean my laptop (phone!) has to have a light bright enough to be seen by a detector 100m away?
This was explained to me a while back: Data transmission is achieved by modulating the light levels very quickly (rather than simple on/off). It can therefore operate in very low light levels (invisible to the human eye) albeit with a bandwidth penalty. Still, this would allow the system would operate in a “dark” building.
> What happens when the phone's in my pocket?
Nothing :) Seriously though, I don't think personal mobile devices are likely to be viable for this kind of technology, but I could be wrong...