Combinations of sheet polarizers and colour filters form the basis of numerous products *RF 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 isotrophic 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, isotrophic-to-polarized conversion efficiencies approaching unity could be attainable by this approach.