Optical systems are described that have at least one source of a beam of blue light with divergence under 15°. A phosphor emits yellow light when excited by the blue light. A collimator is disposed with the phosphor and forms a yellow beam with divergence under 15°. A dichroic filter is positioned to transmit the beam of blue light to the phosphor and to reflect the beam of yellow light to an exit aperture. In different embodiments, the beams of blue and yellow light are incident upon said filter with central angles of 15°, 22°, and 45°. The filter may reflect all of one polarization and part of the other polarization, and a polarization rotating retroreflector may then be provided to return the unreflected light to the filter.