The "light fixture" was designed to be an extra step in the secret room solution. The problem was that it was so close to your feet that it is easily overlooked. You cannot interact with any room items in the dark.
The clapper.
It it in the secret passage in the detention room on Big Nate Island.
get the bell clapper
by the green cabnit and what is useful in the secret room is the bell clapper
The missing bell clapper is hanging from the ceiling.
The missing bell clapper on big nate island is in the secret room under the detention room turn on the light and go to your right and jump on the tool table and above you is the missing bell clapper just jump at it and it will go into your items.
The missing bell clapper on big nate island is in the secret room under the detention room turn on the light and go to your right and jump on the tool table and above you is the missing bell clapper just jump at it and it will go into your items.
Get the clapper. Then go out and put the clapper on the bell (outside of the school)
hanging on a key ring
Find the bell clapper in the secret room under the detention room, and repair the bell. (see the related question)
in the secret room in the school (in the locker!)
Get detention for chewing gum, then go to the entrance of the secret room and find the bell clapper. Put it on the bell and the girls will leave,