lightpipe

Lightpipe, or light pipe, is an optical conduit that transmits light from a source to another location with minimal loss by guiding it through total internal reflection. It can be solid, such as a rod or slab made from acrylic (PMMA), polycarbonate, or glass, or hollow with a reflective inner surface; ends are polished to improve coupling.

Guiding relies on the refractive index contrast between the core and its surroundings. Light enters at one or both ends from a LED or lamp and travels along the pipe, bending as needed, while attenuation depends on material, surface quality, and geometry. The numerical aperture defines acceptable entry angles.

Typical applications include backlighting and indicators in consumer electronics (keyboards, displays, front panels), automotive instrument clusters, and architectural lighting. Light pipes also route light around obstructions or place a light source away from the illuminated area.

Advantages include flexible routing, compact form factors, and easy integration with LEDs. Limitations include loss over distance, coupling losses, potential color shifts with angle, and sensitivity to surface finish and bends. Variants include solid light pipes (rods or slabs) and hollow pipes with reflective coatings; designs may be edge-lit or side-lit.

Light pipes are related to, but distinct from, fiber optic cables used for communications, as they are optimized for illumination rather than data transmission.