The site of Dendera is extremely old, possibly pre Dynastic, with the current temple a rebuild of a much earlier one devoted to the Earth Mother. The Zodiac is unique, as is that carving, therefore it may be a one-off. It could be a representation of a story handed down from eons before, and refer to something that perhaps even the carvers did not fully understand. So, I would not dismiss your idea of a lost technology quite so quickly as some.
It certainly could be argued that the carving depicts a tube of sorts, a plasma discharge, a base, a lead and a storage unit connected to some sort of devices. The interesting part is the depiction of a djed pillar.
It looks nothing like a sarcophagus lid. If it was a depiction of Atum and creation, then why are there two Atums? Soot on the ceiling came from thousands of years of fuel-burning torches and lamps used by others long after the Ancient Egyptians had left the temple.
As far as a lost possible technology is concerned, observe the following two images. If one was to erect a Djed Pillar comparable in size so as to fit into the sockets which were constructed by the Ancient Egyptians, and the Djed Pillar was not part of Osiris's backbone as claimed by the Old Antiquarians, but was an integral component of a power set-up, how much power would be in question? I would venture to say, a darn sight more than is needed for a light bulb.