The brightness of a black hole due to gravitational lensing

The influence of a Schwarzschild black hole on the light from stars is examined. The result is, that due to gravitational lensing light comes from the black hole and thus a black hole shines. The effect is very small and numerical calculations suggest that the magnitude of the black hole is smaller than 60 ^m , this means unobservable with present instruments. It is also shown that there is no effect on the cosmic background radiation.