The word limbo conveys the idea of a land of nowhere, out of sight. Jokingly we can say that instead of a limb like a beam of light there is now a zero, the opposite.

Let us find support from English Etymology:

limb¹ ... part of the body, spec. a member such as the arm, leg, wing; branch (l. of Satan, etc., imp, mischievous person; in OE. dēofles limu 'devil's limbs'; whence simply limb ...

limb² ... A. †limbo of Hell ... B. edge or boundary of a surface or instrument ...

limbo ... region on the border of Hell ... prison, confinement ... neglect, oblivion ...

Significantly there seems to be a hole at this boundary border:

limber² ... pl. holes in timbers for the passage of water ... (O)F. lumière ... light, hole ...