Why are street lights turning purple?

https://youtu.be/4Mll-YDDAF4?si=w5BGeAikiYnhNjU8

4:31 The phosphor coating (that adds yellow color to the light emitted) is falling off but it can be repaired by 11:38 painting back on.

When the phosphor falls off, most of the light is now 9:41 invisible to the eye, so luminance goes way down.