The truth of the situation is the exact opposite, however. These devices do not emit "light" so much as suck "dark". It is based on this hypothesis that they should be referred to as "Dark Suckers".
The more scientific explanation is as follows. When an electrical current is applied to a Dark Sucker, a small opening is torn in the space/time continuum to which "dark" is extremely attracted. Needless to say, the closer one gets to an activated Dark Sucker, the less dark is present.
Those skeptics who try to refute this theory like to call on the presence of heat around a "light bulb" when it is operating. The physics of the reaction bear the theory, despite argument to the contrary. When "dark" is compressed through the space/time rift, the compression causes an exothermic reaction (the same way the compression of gases in an internal combustion engine does).
In conclusion, when a Dark Sucker ceases to operate ("burns out" in light bulb parleyance), it has actually consumed the maximum amount of dark that it possibly can (one could say that it has become full). When this happens, there is no recourse except to replace the full Dark Sucker with a new, empty unit.