  Derived from semi-classical quantum field theory in curved spacetime, Unruh
effect was known as a quantum effect. We find that there does exist a classical
correspondence of this effect in electrodynamics. The thermal nature of the
vacuum in correlation function for the uniformly accelerated detector is coming
from the non-linear relationship between the proper time and the propagating
length of the electromagnetic wave. Both the Coulomb field of the detector
itself and the radiation supporting the detector's uniformly accelerating
motion contribute to the non-vanishing vacuum energy. From this observation we
conclude that Unruh temperature experienced by a uniformly accelerated
classical electron has no additional effects to Born's solution for laboratory
observers far away from the classical electron.
