Distortion of the SED of High-z Luminous Infrared Galaxies by Strong Lensing

We present a model to estimate the effect of differential magnification on the SED of high-z ULIRGs. It is found that the ratio of the high temperature component to the low temperature component can vary with up to a factor of ten with source position on very small angular scales ~0.01". This means that a correction for differential magnification is needed when deriving dust properties from strongly lensed sources.