  Near-infrared (NIR) K' images of a sample of five low surface brightness disc
galaxies (LSBGs) were combined with optical data, with the aim of constraining
their star formation histories. Both red and blue LSBGs were imaged to enable
comparison of their stellar populations. For both types of galaxy strong colour
gradients were found, consistent with mean stellar age gradients. Very low
stellar metallicities were ruled out on the basis of metallicity-sensitive
optical-NIR colours. These five galaxies suggest that red and blue LSBGs have
very different star formation histories and represent two independent routes to
low B band surface brightness. Blue LSBGs are well described by models with
low, roughly constant star formation rates, whereas red LSBGs are better
described by a `faded disc' scenario.
