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Message: <blockquote data-quote="Kevin Purcell" data-source="post: 1527789" data-attributes="member: 68323">Kevin McC:Yeap, you see the variation in direction!The time of day and the direction you look (with respect to the sun) all make a big difference. If you tried this at midday in summer you might not notice the issue. But nearer sunset, opposite to the sun, and in fall you see big effects.I think few people notice this effect though you can see skylight polarization with sunglasses scanning the sky. And bees (and some birds) seem to use it for navigation too!I know you'd know the crossed polarizers "trick". Crossing the polarizers reduced the transmitted light to "zero". But the effect I'm trying to demonstrate is a bit like using crossed polarizers in a geological microscope to pick out mineral crystals.  When you put something between the polarizers that rotates the angle of the polarization light then gets through and the sample lights up. It shows how the bins will rotate the direction of polarized light (because that set up now lets light through) and how it varies with the rotation of the roof prism.FrankD: Yes ... all polarized sunglasses plus a polarized light source will give this effect strongly. It's a bit weaker without the external polarized light but you still get an "odd" effect.</blockquote>