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Fig. 60 shows another form of bulkhead fitting designed to economise lamps. As will be understood, it is fixed in a hole cut in the bulkhead to receive it, say between two cabins, the flange shown being screwed to the woodwork, and the light showing on either side. This fitting is most frequently used where a permanent light is required. It would hardly do for cabin lamps, except in special cases—as, though it could be arranged for a switch in either cabin to turn on the light, neither could turn it off if the switch in the other cabin was closed, which would hardly be convenient for an officer who wanted to turn in during his watch below, if his light happened to belong to the next cabin too, and the owner of that cabin to want the light burning.” (p. 152)
In fact a pair of double-pole double-throw switches can be used to enable either switch to change the state of the lamp at any time, but the real problem with a shared light is of course social, not technical.