  In the present paper, we study the thermal properties of the geometrically
thin accretion disks surrounding the null naked singularity (NNS) and the first
type of Joshi-Malafarina-Narayan (JMN1) spacetimes and compare the results with
the accretion disk around equally massive Schwarzschild black hole. First, we
examine the properties of the circular orbits in these spacetimes. The emitted
flux, radiation spectra, disk efficiency, and temperature distribution on the
disk surface are then investigated. The efficiency of the conversion of the
accreting matter into radiation is found to be substantially higher for naked
singularities than that for black holes. We also verify that the flux radiated
from the disk surface is greater for null and JMN1 naked singularities than
black holes. Hence, the accretion disks around naked singularities are much
more luminous than the black holes of the same mass and accretion rate. In the
luminosity spectra of the NNS, we find that the significant contribution of the
low-frequency is coming from the nearby regions of the NNS. Furthermore, the
spectral luminosity distribution for the "non-zero torque" at the inner
boundary is also analysed by the inclusion of the non-zero torque value at the
inner edge of the disk. The slopes of the luminosity distribution with respect
to frequency for naked singularity spacetimes differ significantly from those
of black holes. These unique features of the naked singularities serve as an
effective tool to distinguish them from the equally massive black holes.
