FAQ: “Do you sell a depolarizer for my HunterLab sphere instrument? On occasion we test polarized samples and there is definitely a dependence on the orientation of the lens. I was wondering if adding a depolarizer would eliminate this phenomenon?”
A depolarizer will probably not help. We do test for polarization in the instrument sphere design and do everything we can to minimize it.
Most of our sphere sensors have pre-mixing spheres around the lamp to homogenize the emitted light. This well-mixed light is then pumped out into the 150 mm (6 in) diameter main sphere which further homogenizes the lamp illumination, minimizing polarization effects.
However, there are still elements in the optical path that can contribute some polarization that can produce an orientation bias in highly polarizing samples like you lenses. All spectrophotometers typically have gratings in the optical path that will have some slight tendency to polarize. Some optical paths also have mirrors which also have slight polarization tendencies.
The best approach to minimize the effect of polarization in color measurements of highly polarizing samples is:
- Fix the orientation of the polarized sample and always make measurements of product standard and sample colors in the same orientation.
- Take readings of a highly polarizing sample in groups of 2 with a 90 degree rotation between each reading. This will average out polarization effects.