Install the diffusing filter. The light rays of a halogen lamp are made of a great number of waves. Each of these waves is characterized by a propagation direction and a vibration of wavelength lambda perpendicular to the direction. With normal light, the vibrating part is of equal intensity in all directions. The light is said to be unpolarized.
Some substances have a property called dichroism.
These substances can favor a plane of vibration so that the light emerging from the substance is all vibrating in the same plane. The light is said to be polarized. There are many ways to obtain polarized light. The simplest and most economical option is to use polaroid filters. The filters are made of parallel oriented microcrystals frozen in a plastic matrix.