Colours Effects on Road Signs
The surface of reflecting road signs under the right illumination not only forms a heiligenschein, but also coloured primary and sometimes secondary bows resembling a rainbow. They are produced by tiny glass elements embedded in the sign surface to increase its reflectivity. They are best when viewed at an oblique angle.
Below: Colour effects on a large road sign with a low sun. The bows are sometimes incomplete because large signs are often made in several pieces with their reflective components differently aligned. Fuji Finepix S2 Pro, processed with Adobe Photoshop Elements
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