  We present a general method to detect nonclassical radiation fields with
systems of on-off detectors. We especially study higher order correlations for
the identification of nonclassical radiation. This allows us to directly
characterize quantum correlations by the statistics measured with systems of
on-off detectors. Additionally, we generalize our method to multiple detector
systems for measurements of correlations between light fields. We also consider
multi-mode radiation fields and isolate nonclassicality in terms of the space
time correlations. Finally, we present results for the quantum statistics using
on-off detectors operating in nonlinear detection modes.
