Glowing effect on foreground blocks: Ash Block (top) and Gray Brick (bottom) both with Diamond Gemspark Walls behind them (left) vs no walls (right).
Gemspark Walls are the wall equivalent of Gemspark Blocks, and come in Online and Offline variants. Like Gemspark Blocks, Online Gemspark Walls emit light but do not count as a light source for NPC housing. Unlike Gemspark Blocks, Gemspark Walls do not act as Mechanisms and their online and offline states cannot be switched after being placed. Online Gemspark Walls placed behind blocks will cause the blocks to appear fully lit, similar to the effect of Illuminant Paint.