Why are LEDs in my home unaffected by voltage drop?
Your LED bulbs are most likely fitted with a wide-range power supply, operating from 100-240 Vac. Hence, when the voltage dropped, they were still within their operating limits and your LED bulbs were as bright as before.

Side note: You'd be surprised how many bulbs marked 220-240 Vac can actually operate down to 100 Vac or less. The nameplate numbers only tell you where it can operate, not where it can't.