second it results in improved polarizing beamsplitter performance according to calculations the performance improvement significantly obviated the necessity for a trim filter at the light valve and the exit windows the 90 u00b0 twist improves performance because the performance of most currently available polarizers is such that polarization by transmission is more effective than polarization by reflection that is the prepolarizer 64 reflects s polarized light through the red filter 70 and transmits p polarized light through the green filter 72 unfortunately some p polarized light is also reflected to the red filter 70 this means that without the 90 u00b0 twist red s polarized light and green p polarized light would be delivered as the main polarizer 44 and since for reasons of economy the main polarizer 78 has the same design as the prepolarizer 64 the main polarizer 78 would similarly reflect some green p polarized light to the red light valve this necessitates the use of a light lowering red trim filter in front of the red light valve to remove the reflected green p exacerbated by the fact that the transmission of green p polarized light to a green light valve in the off state will result in the reflection of the green p polarized light back to the.