ELI5 LED Bulbs - why did the blue LED win a Nobel Prize?

What is so special about the blue variety of LED? Why do LEDs still get so hot if they are supposed to be energy efficient? If LEDs were invented in the 1960s, why have they only become popular in the last decade or two? Why did the blue LED warrant a Nobel Prize in Physics?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community as always and in particular the following users whose questions and comments formed the basis of this discussion: laser_lens_4, spud4, jtw24, brierrat, loderman, audigex, chickencereal, agouti & emblem619 To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected]