  The reflectance of graphene is investigated in the framework of the Dirac
model with account of its realistic properties, such as nonzero chemical
potential and band gap, at any temperature. For this purpose, the exact
reflection coefficients of the electromagnetic waves on a graphene sheet
expressed via the polarization tensor and ultimately via the electrical
conductivity of graphene have been used. The reflectance of graphene is
computed as a function of frequency and chemical potential at different
temperatures and values of the band-gap parameter. The minimum values of the
reflectance are found which are reached in the infrared domain at the points of
vanishing imaginary part of the conductivity of graphene. For a gapped
graphene, the maximum reflectance equal to unity is reached at the points where
the imaginary part of conductivity diverges. The computational results
demonstrate an interesting interplay between the band gap and chemical
potential in their combined effect on the reflectance. Specifically, there are
wide frequency intervals where the reflectance of graphene increases with
increasing chemical potential and decreasing band gap. The numerical
computations are found to be in good agreement with the analytic asymptotic
expressions in the regions of their applicability. Several technological areas,
where the obtained results could be used, are listed.
