  Using the Kerr-Schild formalism to solve the Einstein-Maxwell equations, we
study energy transport due to time-dependent electromagnetic perturbations
around a Kerr black hole, which may work as a mechanism to illuminate a disk
located on the equatorial plane. For such a disk-hole system it is found that
the energy extraction from the hole can occur under the well-known
superradiance condition for wave frequency, even though the energy absorption
into the hole should be rather dominant near the polar region of the horizon.
We estimate the efficiency of the superradiant amplification of the disk
illumination. Further we calculate the time-averaged energy density
distribution to show explicitly the existence of a negative energy region near
the horizon and to discuss the possible generation of a hot spot on the disk.
