Mmm.. about PN100

sorry sirs,ma'ams,

I do a lot of reaserch about the PN100..in youtube and google..Yeah I got an answer on google...but it seems like i dont understand this http://www.futurlec.com/Transistors/PN100.shtml ... and i got no answer from youtube..http://www.youtube.com/results?search_query=PN100+tutorial

 

I just really want to know about its purpose on the IR compound eye of Sir Oddbot..Cause, I do really study all things realted into a stuff

 

I would just like to beg your answers, 

 

-VerDe