sodium-vapor lamp vs sodium-vapour lamp

sodium-vapor lamp and sodium-vapour lamp both are nouns.

Word	Noun	Adjective	Verb	Adverb
sodium-vapor lamp	Yes	No	No	No
sodium-vapour lamp	Yes	No	No	No

As nouns, sodium-vapor lamp and sodium-vapour lamp are synonyms defined as:

sodium-vapor lamp and sodium-vapour lamp: lamp in which an electric current passed through a tube of sodium vapor makes a yellow light; used is street lighting

sodium-vapor lamp (noun)	sodium-vapour lamp (noun)
lamp in which an electric current passed through a tube of sodium vapor makes a yellow light; used is street lighting	lamp in which an electric current passed through a tube of sodium vapor makes a yellow light; used is street lighting