> Sodium lights aren’t even orange in the normal sense of the word. They only emit one wavelength.
It's hard to think of a more normal sense of the word "orange" than "emitting and/or reflecting predominantly wavelengths between 590 and 620 nm." I guess you could argue that sodium is close enough to that lower edge to be yellow?
Low-pressure sodium lamps emit a single wavelength and they are the only kind of lamp that does not use LEDs, but which can match or exceed the energy efficiency of LED lamps. However, with low-pressure sodium lamps you cannot perceive any color.
There are also high-pressure sodium lamps. They emit a broad-spectrum light, even if with an excess of orange-yellow light. You can perceive the colors of things with such lamps, even if not very well. However the high-pressure sodium lamps have a much lower energy efficiency than LED lamps.
In Europe I have encountered mostly, or perhaps only, high-pressure LED lamps used for public lighting. I have used at home some low-pressure sodium lamps for certain purposes, but I am not sure if I have ever seen one like that used in a public space, here in Europe.
Low-pressure sodium lamps typically use transparent glass bulbs, like incandescent lamps or any other kind of low-pressure gas-discharge lamps, e.g. neon lamps.
High-pressure sodium lamps use special bulbs made of translucent alumina ceramic, because glass would not survive in those conditions.
What is the normal sense of the word? I only know the CIE standard observer to define colour and with this it is clearly in the equivalence class of orange.
I think they mean they don't emit a "natural" orange (like an orange flower) that is really some kind of sum of many wavelengths. I could be wrong though.
A pure orange contains only light with a single wavelength.
A mixture of light with different wavelengths that is perceived as orange cannot be distinguished from a mixture of some pure orange with a certain amount of white light.
So any orange, of a flower or of anything else, has the hue of a single wavelength, but it may be more or less saturated, appearing like light with a single wavelength mixed with some white light.
Low-pressure sodium lamps emit a pure color that belongs to the yellow-orange range, so you could describe it as a yellowish orange.
High-pressure sodium lamps have a desaturated orange color, i.e. light that looks like a mixture of orange and white lights.
The orange of any kind of sodium lamp is much more yellowish than the reddish orange of neon lamps with cathodic light, like those used in neon indicators.
Most sodium lamps contain some neon for starting, so when they are switched on they may emit a reddish orange light for a short time, then change to a yellowish orange light, when the sodium vapor takes over from neon.
It's hard to think of a more normal sense of the word "orange" than "emitting and/or reflecting predominantly wavelengths between 590 and 620 nm." I guess you could argue that sodium is close enough to that lower edge to be yellow?