(at around 1h 11 mins) Carol's line "I've seen you naked! You think I wouldn't recognize you because you covered your cheekbones?" was an ad-lib by Blake Lively.
Ryan Reynolds met his wife Blake Lively on the set of this film. They would get married in September 2012 and later have four children.
Ryan Reynolds, who played the protagonist, famously hated the movie. He has admitted to having a poor working relationship with director Martin Campbell and was glad to see the film perform poorly critically and financially, as he did not wish to reprise his role as the Green Lantern. In his later movie Deadpool (2016), he references the Green Lantern in a negative way when he requests a suit that is neither green nor animated while being rolled into the medical room on a gurney; in the sequel Deadpool 2 (2018), he goes back into time, preventing himself from ever taking the Green Lantern role. However, in a 2021 tweet, Reynolds re-watched the film, and admits that his opinions on the movie have changed to a more positive verdict.
To prepare for his role as Hector Hammond, Peter Sarsgaard spent time with a biologist from Tulane University, who he described as "the most eccentric guy I could find." They both worked on preparing the lecture Hammond gives in the film.
One of the Green Lanterns, Rot Lop Fan, wears a bell insignia rather than a lantern image on his chest. This is because his world gets almost no sunlight, so they never developed eyesight. Since he has no use for colors and lights, his symbol is an F-Sharp bell, which makes a tone pleasing to his species.