Light Suppression in Minecraft 1.13 and below. Why hasn't this been found before?


1.14+ light suppression by Kayleigh, and further developed by Viktor, vktec, etc.
1.14+ explanation by vktec: https://www.youtube.com/watch?v=JtoTAkjpuHA
1.14+ showcase by Viktor40: https://www.youtube.com/watch?v=0ZiU_pcmoEE
(original credit for 1.14+ light suppression is disputed, the above credit is the result of a best-effort investigation by me.)