A: There is a great deal of debate on this issue. Up until the mid-20th century, the accepted answer was ‘one’: and this Whiggish narrative underpinned a number of works that celebrated electrification and the march of progress in light-bulb changing. Beginning in the 1960s, however, social historians increasingly rejected the ‘Great Man’ school and produced revisionist narratives that stressed the contributions of research assistants and custodial staff. This new consensus was challenged, in turn, by women’s historians, who criticized the social interpretation for marginalizing women, and who argued that light bulbs are actually changed by department secretaries. Since the 1980s, however, postmodernist scholars have deconstructed what they characterize as a repressive hegemonic discourse of light-bulb changing, with its implicit binary opposition between ‘light’ and ‘darkness,’ and its phallogocentric privileging of the bulb over the socket, which they see as colonialist, sexist, and racist. Finally, a new generation of neo-conservative historians have concluded that the light never needed changing in the first place, and have praised political leaders like Ronald Reagan and Margaret Thatcher for bringing back the old bulb. Clearly, much additional research remains to be done.

[This is from historian David Leeson, shared on Facebook]