How to use SMD LEDs to replace through hole LEDs, this app note (PDF) from OSRAM discusses about light guides/pipes, backlighting and lenses to channel its display efficiently.
The use of SMT-TOPLED varies greatly from the use of traditional through hole LEDs. Historically through hole LEDs have been incorporated directly into front panels using the leads as a stand. Due to the automated nature of SMT assembly, and the size constraints of SMT component and assemblies, SMT-TOPLED applications are different from through hole applications. For SMT applications the LED is often 10 mm or more from the front panel. Employing light guides can create the optimum display to the final viewer. Because of the size and radiation pattern of the Osram Opto Semiconductor SMT-TOPLED the final light emitting surfaces can be created in almost any shape. Lenses can also be combined with SMT-TOPLED. Because of the uniform repeatable radiation pattern, the lens design can be matched to the exact customer requirements. Additional applications include backlighting of symbols and liquid crystal displays.