The paper shows that the Wigner distribution function of quantum optical co
herent states, or of a superposition of such states, can be produced and me
asured with a classical optical set-up using classical coherent light field
s. This measurement cannot be done directly in quantum optics since the qua
ntum phase space variables correspond to non-commuting operators. As an exa
mple, the Wigner distribution function of Schrodinger cat states of light h
as been measured. It is also shown that the possibility of measuring the Wi
gner distribution function of quantum coherent states with classical cohere
nt fields is unique in the sense that it cannot be extended to other quantu
m states, not even to the incoherent limit of the superposition of coherent
states.