Block that exceeds a light level of 15?

I want to make a block that is brighter than any block from vanilla Minecraft. I tried editing the code to change the light level from 15 to 20, but it broke and emitted no light whatsoever in-game. I know I could achieve this by making it spawn light blocks around itself, but that workaround would be annoying to do and could create problems down the line. Is what I'm trying to do possible? Thanks.