Luas is a different gauge to Irish 'heavy' rail = TRUE. 1400mm was chosen to enable ready-built trams to be bought.
Green line trams can't run on the Red line = FALSE. While Green line trams are 10m longer, the articulation allows running of any Luas tram on any line.
Luas couldn't go across Dublin because the corner of Nassau Street and Dawson Street is too tight (Garrat FitzGerald) = FALSE. The articulation of the Citalis tram can take this corner.
Luas the movie!
This is a link to a directory containing some movie images of Dublin's Luas, a "driver's eye" view. I don't know if there are many movies of the Luas and hope you enjoy these. Before you think about downloading these movie clips, please consider the following:
Full detail may be found on the page: Luas the movie(s)!