The lights use ultraviolet LED's to activate a phosphor that results in white light.
This phosphor is degrading so you are seeing the UV light.
Why are streetlights on the highway purple?
The Florida Department of Transportation has replaced 800 of the defective streetlights on central Florida highways, with 200 still needing replacement. The timeline for completion is uncertain, though it was originally predicted to be finished last April.
The issue is caused by a spectral shift in the bulb or filter of the "autobahn" model light heads, supplied by American Electric Lighting under Acuity Brands, that is experiencing a color change caused by phosphorous in the device.
Acuity Brands stated that the light output is in no way harmful or unsafe and that they have proactively worked with customers affected by the issue to resolve concerns. FDOT is not the only agency replacing the defective streetlights; power companies, including Duke Energy, are also replacing the lights.