Sort of related to other posts about power cuts but not quite,

I recently have had my attention drawn to the 'Blackout bulb' A normal looking LED lamp for a Bayonet or ES holder, but with a battery inside. When mains is present it lights normally and charges the internal battery. If mains is cut and the bulb 'sees' a  high impedance, such as a normal light switch, then it goes off. So far so good, now the clever part..

If the supply fails, but there is a low enough resistance between the terminals, such as in a power cut, when other loads will be in parallel, then the light comes on using the internal battery (*). Claims to run for up to 3 hours.

I can see a use for these to retrofit for  landing lights and similar places where an EM fitting may  not be that convenient.

Has anyone else used them  yet ?

Would anyone dare suggest they could replace normal EM fittings ?

Mike.

(*) a moist finger is enough to get it started and you can use it as a hand held lantern