The designer of street lamps, is either aware that a sidewalk is near the street they are trying to illuminate or the other way around. But when the two worlds collide interesting results appear. The two difference requirements are visible in the lamps design.
Sidewalks require brighter more intense lighting, how is this accomplished? Lowering the light. This provides for a double tiered design. That seems to be all over Barcelona, almost ubiquitous within the ensanche.