I have a single circuit breaker for all lighting circuits in my apartment unit. However I'm having severe voltage drop in my bedroom's light sockets. I started suspecting about it ever since the brightness of the bulbs became unbearably low even after recently just changing them.
My bedroom has two light sockets both with a separate switch but placed in a single enclosure. With my multimeter, I only get about 110V on each socket (we're in a 240V country). However, the voltage reading weirdly rises to about 150V when I switch on one bulb. So I get these bulbs which are very dim when only one of them is turned on but slightly gets brighter when both of them are on.
I already changed both the switches (I thought the switches are causing a high resistance fault) but unfortunately, the problem still persists. It is also important to note that this problem only occurs in my bedroom. The voltage from light sockets in my bathroom, living room, kitchen, and dining area are fine at about 240V.
EDIT 1 I'm from the Philippines and some regions have split-phase power and some don't. I'm from a region which has split-phase power. But although that's the case, using 120V is extremely rare here. So in a typical home here, all circuits (including lighting) delivers 240V in split-phase. I confirmed that my lighting circuit also has 240V split-phase after seeing that it uses a dual pole circuit breaker. I also haven't seen any neutral wire inside the switches' box.