[1] Musically, "Spectrum" is a downtempo orchestral pop,[2] R&B,[3] krautrock[4] and disco song with drums while backing vocals repeatedly sing "Say my name" throughout the choruses.

While reviewing Ceremonials, Jillian Mapes of Billboard complimented Welch's vocal performance, stating, "'Say my name,' she howls then later croons, both filled with sensuality.

"[6] A writer of Rolling Stone praised the song calling it "a huge, churchy tune, even in the context of the band's typically bombastic blend of arena rock and gospel.

"[7] Lewis Corner from Digital Spy gave the song four stars out of five, saying "if there's one thing latest single 'Spectrum' proves, it's that she knows how to write a distinctive uptempo number without compromising her style.

"[8] He added that the song "[...] belts over a rapturous chorus complete with rousing piano and delicate strings – demonstrating that techno synths are not the only key to a euphoric hook.

"[14] During an interview, LaChapelle also spoke about his collaboration with Welch, "It's a beautiful song that really touched me and inspired me to create imagery that matches its power.

A writer of Rolling Stone wrote, "Music video legend David LaChappelle rose to the challenge of making a clip for the song, matching its drama and energy with a vivid color pallette and incredibly theatrical staging.

[citation needed] On 12 September 2012, Florence performed a stripped-down version of the song on Late Night with Jimmy Fallon.

[17] British DJ and producer Ilan Bluestone played a mashup of Spectrum with his song "Under My Skin" during his live set at Madison Square Garden for Above & Beyond's ABGT100 show.

Lewis Corner of Digital Spy commented that "While the single version is near perfection, an accompanying Calvin Harris remix highlights just how big a Florence house anthem can be".

[8] The instrumental version of "Spectrum" was used extensively during the BBC's coverage of the London 2012 Olympic Games, often as the backing track to their round-up of the day's sporting action.

[20] On 15 July 2012, following the release of the Calvin Harris remix of the song, it climbed the chart to become the band's first number-one single in the UK, selling 64,816 copies in its first week.