Mayor Eric Garcetti and LA Police chief Charlie Beck were expected to be at the public event at City Hall, which started about 21:00 local time (05:00 BST).
The signal originated in the DC Comics strip as a sign that the caped crusader was needed to save the day.
West, who also famously donned his cape for the hit 1960s TV show, died last week after a “short but brave battle” with leukaemia, his family said.
Actor Burt Ward, who played Robin alongside Adam West’s Batman in the hit 1960s TV series, also paid tribute to his co-star, telling the BBC that the two had enjoyed “an amazing friendship”, describing the actor as “a lot of fun”.
Animated comedy Family Guy will also honour West this weekend. He played its eccentric Mayor West for more than 100 episodes on the hit cartoon show. On Sunday, US TV network Fox will show the episode The Dating Game, which features West winning an auction for the Medieval Castle restaurant.
It was originally broadcast in March and the show will air a tribute just before the episode begins.
West was in Family Guy from 2000 until this year, voicing Quahog’s mayor – a satirised version of the actor, in the series created by Seth MacFarlane.
MacFarlane paid tribute to the star on Twitter, describing West as “irreplaceable”.