Answers (1)
A light bulb is only approximately described by it's ratings. Actual performance depends on temperature. When the filament is cold it typically draws ten times the rated current. So you have no idea how it will work on 6 volts unless you measure it.
Energy is not a physical unit. It is a philosophical concept and an accounting technique used to analyze mechanical and chemical exchanges. In nuclear physics it is defined as a wavelength of light, in biology it is a synonym for metabolism, and in public utilities they say energy when they mean connectivity. Anybody who uses the word in any other context does not know what he is talking about.