quote:
Get a multimeter and test the socket. The center should be hot and the sides should be neutral. Touch the black wire to the sides and red wire to the center. It should read around 110V. If it's backwards, it would be -110V.
Um...no. Power in your house is 60HZ AC. When a switch is flipped on, voltage is applied. The flow of current starts, increases, peaks, decreases, hits zero, and then switches direction and flows in the opposite direction. It again increases, peaks, decreases, and hits zero. Lather, rinse, repeat. It happens 60 times per second. There is no "positive" and "negative" as there is with DC. If you stick the leads of a voltmeter into the hot and neutral of a receptacle, it should read a nominal 120V. (There is no such thing as 110, 115, or 220 for that matter). If you take the leads out, reverse them, and stick them back into the receptacle, it will still read 120V.
When used to describe generic AC circuits, "polarity" refers to keeping the phase/ungrounded/hot conductors and the neutral conductors referenced to each other in the same way. This is why we now have polarized plugs and receptacles. This helps ensure the switch on the lamp/appliance/radio/whatever is always interrupting the hot as it enters the device. It minimizes the amount of the device that is energized when off. When all wired correctly, it would ensure that the shell of the lamp socket (for example), as opposed to the button or tab at the bottom, gets connected to the neutral. This means if you happen to grab the shell while futzing with the lamp when it's off, it shouldn't bite you.
I've played with the $3 Chinese LED A lamp replacements from HEB, and the $50 Acculamps from Lithonia. The only time we couldn't get one to work was when the damn thing was just a hair to wide/long/fat to fit in the fixture. In some cases, it was literally a bunt hair off.
If the OP's can lights have the metal tab at the base, bend it up and see if it will do anything.
In the meantime, I'd be interested in hearing how a CFL or LED, or more appropriately the CFL ballast or LED driver, is smart enough to tell one side of a 120V AC circuit from the other. I'll hang up and listen.