I mounted a single LED and holder into our ceiling light fixtures with a resistor in line. The wall switch provides power to the fixture and the fixture has a switch built in for the lights. I installed the LED before the switch in the fixture.
When we turn on the wall switch the LED nightlight comes on as well as the regular lights. At night, we push the off button on the fixture and leave only the LED on... the single LED provides plenty of light to get around without blinding anyone.
We installed these on several light fixtures and they've been in service for about a year and a half now with no problems with our smart charger's voltage.
Here's a link to what I did...
Nightlight project.
Happy Camping!
John.