Is it true that one must operate compact spiral fluorescent light bulbs only with the base down not in inverted or horizontal sockets?

No, this is not true. The spiral-type compact fluorescent bulbs can be operated in any orientation provided that there is sufficient air circulation around the bulb. But if you put the bulb in a fixed enclosure then it will last longer if the base is facing downwards so that the heat is conducted away from the electronics in the ballast. Always follow the manufacturers's directions - usually written on the bulb. No, this is not true. The spiral-type compact fluorescent bulbs can be operated in any orientation provided that there is sufficient air circulation around the bulb. But if you put the bulb in a fixed enclosure then it will last longer if the base is facing downwards so that the heat is conducted away from the electronics in the ballast. And, always follow the manufacturers's directions - usually written on the bulb. Regards, Laszlo Herczeg, laszlo DOT herczeg AT austinenergy.com