Optical anisotropy effects in tempered glass can affect the transparency of glass building envelopes in the form of iridescence. Birefringence is created in the standard tempering process and results from even the smallest principal stress differences across the thickness of the glass. Currently, no standard or guideline exists for evaluating optical anisotropy effects in tempered glass. In recent years, photoelastic methods have been developed for full-field, non-destructive measurement of optical retardation caused by anisotropy effects. This study focuses on whether and how the retardation measurements correlate with the visual anisotropy effects under natural daylight in reality. Therefore, quantitative retardation measurements were first performed on various glass panes, followed by qualitative studies to correlate the visibility of the anisotropy effects in an outdoor test facility. The investigation shows that the quantitative measurement of optical retardation and the presented evaluation methods allow the objective evaluation of anisotropy effects.