Combinations of sheet polarizers and colour filters form the basis of numerous products(1-4)-most notably colour liquid-crystal displays(2,4)-that require polarized chromatic light. But this combination of elements does not make efficient use of light, as a substantial fraction of the incident light is converted into thermal energy(3,4), limiting the brightness and energy efficiency of the resulting devices. Here we show that these limitations can be overcome by using polymer-based photoluminescent polarizers. Our polarizers operate on a two-step principle : randomly orientated ＇sensitizer＇ molecules harvest the incident light by isotropic absorption and then efficiently transfer the energy to a uniaxially orientated photoluminescent polymer, from which coloured light with a high degree of linear polarization is emitted. In principle, isotropic-to-polarized conversion efficiencies approaching unity could be attainable by this approach.