Do you have a 12V for the E27 screw? If any, which side is the positive pole? Is it a screw or a tail? I've seen a lot of light cups that don't seem to have a 12V E27, which is a lot of 12V and MR16. Is E27 only 220V? There seems to be no 12V communication, right?
The incandescents are partially negative, with a zero point of fire. The tail nail is the fire line and the thread is the zero line.
I am doing low voltage running maintenance, must have 12V lamp, specific your E27 is not clear, the communication 12V is not positive negative pole, fire line, zero line connect. Advice: 220V light is easier to find and 220.
In accordance with the standards of IEC, E27 lamp holder only primary voltage is 110 v to 230 v, if use 12 v to the E27 lamp holder pressure drop will be bigger, that is to say on the filament voltage will be far less than 12 v. So, 12V is usually directly touched by a light bulb. Like you said MR16, G4, etc.
