I confuse myself frequently here. I apologize if I made any incorrect statements in the past. Hopefully, I can write this clearly, and rely on this documentation for the future.
L = Vanilla Blocklight (kept for backwards compatibility)
S = Vanilla Sunlight (How much sunlight is the block getting... or moonlight)
R = Red Light Channel (Added by CLC)
G = Green Light Channel (Added by CLC)
B = Blue Light Channel (Added by CLC)