
At first these lamps remained dark, while the other E12 LED lamp and the old incandescent lamp installed in a socket worked perfectly. What I noticed on closer inspection is that these lamps (middle lamp in the photo) have electrode tips that do not protrude as far into the socket as the others when the lamp is installed (see yellow arrow). The physical difference is slight, but sufficient to prevent the tip from making contact with the metal rib at the bottom of the socket. After using a dental tool to carefully adjust the base and tip of the tab in the socket, these lamps worked perfectly.