1: I dislike blue LED simply for the fact that they hurt my eyes at night.
2: I use them because I have a surplus of 200 of these demon lights and I do not want to waste something that I like on an experiment. OH... and they tend to photograph really well.
3: You cannot drill a hole deep enough into a glass marble to accept an LED! They always crack at less than 1/8 of an inch
4: the interface between the cut LED and Ground Glass is optically good and gives excellent light transfer to the Marble.
5: The Glass marble is a lens which diffuses the light.
6 This is an LED modification and is used wherever you would use a standard LED. You will connect it as you would any other LED.
So certain I am that you cannot drill a hole deep enough into a glass marble to accept a 5mm LED... that I will gift the first person that can show me a picture of 2 working drilled glass marble LEDs, drilled using supplies available to a regular person at a minimal cost... a 1 year PRO membership to Instructables ( if that is acceptable to the overseers of this excellent site)