mdooher:

 

https://safelumin.com/shop/sa19-800g27-2pk/

 

 

 

You can get theses here, https://waitakere.org.nz/product/safelumin-emergency-rechargeable-cool-daylight-2700k-led-e27-bulb-2-pack/?v=c97b334ffd41very common in South Africa or so I'm told. It works as a standard bulb but when there is a power cut the battery takes over. It knows the light switch is on because it detects the circuit impedance.

 

I.e. it doesn't mater if the utility power available it just works as normal

 

There are various other brands as well

 

So simple, and so clever.