You can also hear just a wee bit of Celtic in the music. This song seems to have all those aspects. Sounds like they were trying to reproduce bag pipe sounds in sections.
Here is some info from Wikipedia on this song, which they never did perform on stage.
The unique sound of the intro to the song was created by Jimmy Page using a violin bow on an acoustic guitar....."In the Light" was never played live at Led Zeppelin concerts.[1] According to Jones, Robert Plant was emphatic about wanting to play the song onstage, but because Jones could not reproduce the synthesizer sound properly outside of the studio, he vetoed the idea.[citation needed]
Plant is still doing pretty well touring with Alison Krauss and singing old classics like "Battle of Evermore". The version from the Tennessee performance was awesome and yes I agree there is a bit of Celtic in some of their music.