What caused the blue lights in the sky?

Neon blue sky in New York caused by transformer explosion: NYPD

Strange blue lights appear in skies across the world as sightings

Blue Light: What Is It, and How Does It Affect Our Eyes?

Freaky blue spiral spotted in Hawaii sky. What was it

People report line of lights in the night sky

Cambs family baffled by 'weird' lights in the sky that made

Strange Blue Lights' Seen Over Arctic Circle Were Not Aliens, Says

Blue Light: What Is It, and How Does It Affect Our Eyes?

Strange blue lights appear in skies across the world as sightings