Google uses WiFi and Bluetooth info for location tracking. So they can track you when you don’t have GPS switched on. WiFi names, MAC address are correlated to locations by google.
So google infers any app that has WiFi or Bluetooth access can track you like they do.
I think it is LED technology. LEDs have a very small bandwidth. Even white leds are just three very small small bandwidth emissions.
The very tight intensity in such a small bandwidth is hard on the eyes. Even when compared with the same power of older lighting technology, which has a comparatively massive bandwidth.
LEDs could be designed to compensate for this better. They could add more different colours of LEDs to the matrix that makes up white LEDs.