Subject: how big is the difference between classical and quantum electrodynamics ?

After reading the book "QED" by R. Feynman I was wondering especially with
regard to the famouns mirror example of Fig. 24 (p.43), where the probability of
detecting photons at point P is derived simply by adding arrows, how big would
be the difference in terms of the length of the total arrow if we try to
calculate the total field at point P via classical electrodynamics based on a
rigorous solution of Maxwell's equations and compare the result with QED ?
I would be also very grateful if you could recommend me some other good books
about QED . Thank you .

Re: how big is the difference between classical and quantum electrodynamics ?