A less light blocking polarizer must be less light polarization.
A light source come from a perfect reflector, such as a mirror glass, is almost fully polarized, ..., the none polarized component is the transmitted, unreflective part. so a fully polarization filter would complete block the light or complete pass the light depends on the rotation of the filter.
In the normal condition, the light source is likely a uniformly mixed of all polarization orientation, the polarization would cut the light into half in terms of EM field strength. Since the light intensity is proportion to the square of EM field, the light intensity would be cut into quarter.
With the same light source the polarizer can be less light blocking and less if it has less polarization capability.
