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Bees are reputed to be able to navigate on cloudy days. I don't know whether they are seeing the sun directly through the clouds, or whether it is because the blue end of the spectrum (incidentally, one of the dichroic colors of corderite is blue) is more strongly scattered and polarized. In any event, bees are able to see UV. So, I would suggest that you put a blue filter on your apparatus and repeat the experiment and if that doesn't help, then move into the UV region and experiment.

Used a digital light intensity meter (Lux) with two 55mm camera linear light polarizes (one would have worked), a Blue cobalt glass filter, and different lengths of cardboard tubes to limit the field of view and amount of side light interference.

Test result analysis. Under ideal clear skies when one samples the sky at about 30-130 degrees from the suns position, one can get an average of about 18% light intensity change using a polarizer and a blue cobalt glass filter, while shielding of side light, using a tube length of 2.5 times diameter. For a tube length of about 1.1 times diameter, using a polarizer and no blue filter I was able to measure an average of about 12% light intensity change when the polarizer was rotated 90 degrees. I estimate, one could measure the suns direction as a projection on the earth's surface, to with in 10-15 degrees using this method on a clear day.

Light level results were measured during relatively thin white uniform cloudy conditions with different rotations of the polarizer. The difference in light intensity due to polarization was measured to be below the noise level of about 1% to 2% with occasional fluctuation up to as much as 4%. The intensity of light from clouds is constantly changing due to the clouds becoming thicker and thinner as they move. This causes a constant fluctuation of overall light intensity of about 1% to 5% over a short time interval making it difficult to measure small changes when the polarizer is rotated 90 degrees. Filtering for blue and ultraviolet does help but not enough to make a difference. It was observed the direction of maximum polarization is random with a slightly higher frequency of occurrence of polarization being perpendicular or parallel to the direction of the sun. However, the effect is small, well below reliable measurements with the current setup.

Offered by Mike.