In the process of designing these levels, I realized that puzzle design is about making players feel they're smart rather than prove designer is much smarter than players. Thus, most of the puzzle is related to using environment such as lighting, visual pattern or color to give players guidance. 

 

Specifically, in my levels, I pay close attention to the lighting and wall type. I deliberately placed the wall that can open portals in the crucial locations to give players some starting point. I also placed some decoration light to help the player aim at a far distance. These helped players finished the level much easier which maintain the difficulty.