Due to quantum fluctuations, particle-antiparticle pairs are created near the even horizon. One particle falls into the singularity as the other escapes. Antiparticles that escape will emit Light when they annihilate with matter.
The heavier the black hole, the less power it radiates.
The Blackbody Radiation and temperature of a black hole are
See Schwarzschild Radius, Stefan-Boltzmann Law
Evaporation
The lifetime of a black hole is: