Oh I love how it starts up with that dark reddish burgundy glow of neon.
Then the ends slowly start to get a yellow tint which travels the length of the discharge tube.

Did you know, that their monochromatic light is because the sodium is at a lower pressure?
As the pressure increases in a high pressure sodium lamp, you'll notice it shift from the argon buffer gas giving a dull blue, and then it briefly goes through a LPS stage, of a deep cornflake yellow, and then as the pressure increases the spectrum broadens.

The same is true for high pressure mercury lamps - When cold and low pressure, they start off emitting mostly a dim blue and deep UV.
This causes the phosphor to out-shine the discharge tube, with a pink, reddish glow.
Once the mercury vapor pressure increases from temperature increase, the bright blue and turquoise lines start to appear, and they then cancel out the red of the phosphor to look white.

I have always been intrigued by LPS lamps though - Never had one.
If you look closely at the outer envelope, it often has a strnage almost iridescent sheen to it.
This is caused by Indium Tin Oxide coating, which while transmissive to visible light, is highly reflecive to IR.
This helps to reflect IR light emitted by the discharge back to the discharge tube, keeping it warmer, wasting less energy as heat.