How lightsticks became a must-have item for K-pop fans

The flicker of tiny lighter flames once illuminated dimmed concert arenas during heart-wrenching numbers. Then it was phone flashlights waving brightly for all to see. But now K-pop fandoms have invented something much more high-tech to demonstrate their love for their idols: lightsticks. 
These bright, beautiful lights are an essential part of any K-Pop concert-going experience. But why would fans pay top dollar for a glorified glow stick they'll only use once in a blue moon? K-Pop fa