Relates to MC-102220, which I would recommend reopening.

Light blocks are blocks intended to be invisible for players outside of occasions that involve placing, destroying or configuring them. It is likely that these blocks will see use in custom structures made with structure blocks. However, despite light locks being classified as an "invisible block" in gameplay terms, they are not considered so by structure blocks, and even if within the structure block's bounds, they will appear invisible nonetheless. As barriers also exhibit this behaviour (see MC-102220), this makes barrier blocks and light blocks hard to distinguish in structures without forcing the player to have these items on hand at all times.