The document analyzes separating direction indicators and stop lamps. It examines how drivers recognize lighting functions through visual perception and notes that irregular lamp shapes increase reaction time. The document states that “apparent surface”, currently defined only through manufacturer drawings, lacks perceptual grounding because it ignores luminance distribution and edge contrast. It recommends minimum lamp sizes and distances based on visual acuity, minimum luminance requirements, and a 3:1 luminance contrast between functions when spatially merged in one lamp.