In contrast to the mainstream interpretation, a fringe hypothesis proposes that the reliefs depict ancient Egyptian electrical technology, based on comparison to similar modern devices (such as Geissler tubes, Crookes tubes, and arc lamps). J. N. Lockyer's passing reference to a colleague's humorous suggestion that electric lamps would explain the absence of lampblack deposits in the tombs has sometimes been forwarded as an argument supporting this particular interpretation (another argument being made is the use of a system of reflective mirrors).