Red Light is the third studio album by South Korean girl group f(x), released on July 7, 2014, by S.M. Entertainment. It reached number 1 on the Gaon weekly album chart and had two promotional singles, "Red Light" and "Milk". This is the last album to feature member Sulli, who left the group one year after the album's release.

The Red Light album has a dark and eerie concept, which f(x) said they liked. Krystal added that she likes this concept because she's often given roles that make her look pretty, and just this once she wanted something that would make her look darker and different.

Naver describes the album's title track, "Red Light", as a "blast of urban rhythm bit, reversal in electrohouse genre". The lyrics talk about capturing great moments, stop and reconsider what is important in life. Also, it is a message, using a “red Light” to symbolize the warning, that is expressed in an eye-catching way.Kenzie, penned the lyrics for the song and Maegan Cottone of Phrased Differently, Daniel Ullmann, Bryan Jarett, Allison Kaplan, and Sherry St. Germain were credited for the song's music. It was produced by Lee Soo-Man and Casper & B. F(x) member Amber Liu describes the song's dance as the "most passionate" and "most dynamic". Member Luna stated that the song's genre fit with their aim for a slightly intense but feminine image.

The title track "Red Light" impacted Korean Broadcasting System's "K-Pop Connection" radio on July 8, 2014.

The group had their debut performance of the album's lead single, "Red Light", on July 3, 2014 through Mnet's M!Countdown. The Red Light album reached number 2 on the weekly Gaon albums chart, while the promotional single "Red Light" went to number 1 on the Gaon weekly digital chart and the Billboard K-pop Hot 100. Several other non-promotional album tracks also charted on the Gaon and K-pop Hot 100 charts, as well.

Red Light debuted at number one on the Gaon Album Chart for the week ending July 14, 2014. The record has sold 86,143 copies in South Korea in 2014, becoming the nineteenth best-selling album of the year.

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