I have found that the american fluorescent and HID that imported to Israel aren't "Export lamps for use outside USA" but instead imported "As are" (As these lamps can't be operated in europe and are for use only in the USA. Literally direct buying of the originl from USA). Ie... original american bases (Ie. Mog E39 and Med [Not E27]) and also they don't passed any european and international standard (They aren't appears at their boxes). I don't know how these lamps with the Mog based can be inserted to E40 sockets and the Med ones to E27 sockets as accurs in Israel, since we haven't any american sockets in Israel except for the HO F96T12 fluorescents.

E26 and E27 are mostly "compatible", E40/E39 i'm not as sure. But biger issue i would expect with ballasts - designed operating currents and required ballast OCV are frequently different in US then in EU for the same wattage.