Metals are (to first order) "equi-potentials". It doesn't matter, to first order, where you measure the voltage drop between any place and on a metal and ground.

So a simple bulb isn't going to know the difference between a switch being off in the lamp or the power being off at the circuit breaker.

So, without some other voltage sense somewhere, it's not going to work as a battery backup light unless the switch between the bulb and the power is on.

We have emergency flashlights at work that are plugged into 120V outlets. When the power is on, the flashlights are off. When the outlet loses power, the flashlights come on. (You can also remove the flashlights and turn them off.)

I assume these bulbs work the same way, but it's hard to think of a use-case that matches using them in a lamp at home. Unless it has, say, a very sensitive Hall Effect sensor (to sense the magnetic fields from nearby AC power lines) or something similar. It does say it has some built-in intelligence, so maybe that's it.

Since it doesn't seem to be available any more, at least not at B&H, perhaps its a moot point. :-)

Cheers,
Scott.