Eu acompanhei este tópico, e frequento este fórum, quanto ao francês, o Pascal Danjou, não participou da discussão, apenas foi citado.
PS: having just exchanged a mail with Pascal Danjou he told me he believes too it is just an electric plug ... but he also don't know exactly what for.
Adding a light in a definite context might indeed be an hypothesis but it could also have been used to provide power to something. For me the question remains open. We will probably learn one day for sure