“You’re telling me I have to go to concerts without fun light-up wristbands after this?” wrote one Taylor Swift fan on TikTok after the US singer’s concert in Cardiff earlier this summe ...

The idea behind the PixMob wristband is simple — at a concert ... infrared projectors are used to transmit commands so they all light up in sync. Sometimes, attendees would be allowed to ...

WSJ goes behind the scenes with one LED company, PixMob, to see the tech behind the wristbands. Photo illustration: Madeline Marshall ...