Purple is a combination of wavelengths from opposite extremes of the spectrum, which technically deosn’t make any sense, but ...

Some photographers have made a project out of chasing the unique aesthetic. (This story has ... from streetlights that were producing the purple light, using both microscopic and thermal analysis.

The purple lights are not for aesthetics. They're a manufacturing defect. The coating on the phosphor layer, which blocks blue wavelengths, is wearing out, throwing off the color of the light.