Problem on the third floor

Okay, I've just come up on the elevator and it's my first time on the third floor. I've tapped on the lantern (i'm playing on an iPad) and picked up the note. I know I'm meant to light up the room with my fireflies, but I can't find anywhere to put them! I think I have all the fireflies from the second floor, having made three collections in different rooms, but is there something else I need to do? I guess until I light the room properly, I won't be able to play the HOS, but no matter where I try to place the fireflies, I just keep getting told I'm "using the item incorrectly". Aaaarrrgh!

Problem solved! As so often happens when I post a question, I went back to the game and solved my problem immediately - apparently I didn't tap firmly enough on the lantern first time round.