The second kind of perspex is transparent like glass. In this case the light of the bright pointed led directed forwards has to be broken to other directions.
That is why in these transparent add-ons there are little round shapes and lines in the center line of the led beam.
The shapes are made with Illustrator and exported as a dxf file, which can be used for the laser cutter.
Some of the ai files can be found here: http://contrechoc.com/blogProjects/led_3mm.zip
Of course other types of perspex can easily be used, like colored perspex. Experiment!