Sodium.
Na.
A chemical element I'm certainly familiar with.
Gaseous Na, heated in a planetary atmosphere to 2000 degrees F, ionized
by intense ultraviolet light from the nearby star, would glow like a street-lamp.
A good analogy, since many cities
rely on night-time illumination by using sodium lamps.
The planet's upper atmosphere would
have an amber glow, assuming other chemical substances or elements
weren't mingled with the sodium
to generate other glowing colors.
Jake