To ensure light is effectively captured from the LED and delivered to the desired location, it is essential that the light pipe cavity is properly designed for the matching LED. This will ensure that all the light is trapped within the light pipe and travels through the light pipe rather than escaping out into the environment.  LED size will vary in applications, though commonly the LED size will be about 1.6 mm x 3.2 mm (as in the Lumex 1206 LED series). A smaller size will typically be around 1.5 mm x 1 mm and larger sizes are often about 3 mm x 3 mm.