A photomultiplier (PMT) has a dark count noise level of 100 counts per seconds. Calculate the minimum optical power \((S N R=1)\) at \(500 \mathrm{~nm}\) that can be detected within a \(10 \mathrm{~s}\) integration time. Assume a quantum efficiency of 0.2 at \(500 \mathrm{~nm}\).