Our condo building switched over to LED tubes years ago from the florescent type and installed a special type of LED tube that bypassed the ballast, so I was told. In other words, it appears that these new LED tubes use 115 volts, and one end is marked "AC end" (not sure what that means). But to my surprise, when I went to change one of the new tubes with an LED tube I had of my own, it didn't work. How many different LED tubes are there on the market, so that I can order the right ones?