Tell us about yourself!
yeah, 10% sounds about right, you lose half of the light in the polarizer, and two thirds of what's left in the colour filter you'd get 16% with ideal parts ans a perfect light path. If you can replace the color wheel with coloured LEDs you could improve matters threefold.
there's no need for a single point source, it's not a shadow box. just get the light to go through the LCD evenly and into the lens.