  The perturbation of a light field might affect preheating and hence generate
a contribution to the spectrum and non-gaussianity of the curvature
perturbation \zeta. The field might appear directly in the preheating model
(curvaton-type preheating) or indirectly through its effect on a mass or
coupling (modulated preheating). We give general expressions for \zeta based on
the \delta N formula, and apply them to the cases of quadratic and quartic
chaotic inflation. For the quadratic case, curvaton-type preheating is
ineffective in contributing to \zeta, but modulated preheating can be
effective. For quartic inflation, curvaton-type preheating may be effective but
the usual \delta N formalism has to be modified. We see under what
circumstances the recent numerical simulation of Bond et al. [0903.3407] may be
enough to provide a rough estimate for this case. This paper is dedicated to
the memory of Lev Kofman who died on 12th November 2009
