If it dropped from 8 to 7 it means you've seen an event. The lightbulbs are exclusively meant to tell you that you have all the requirements for an event, minus the items. Keep collecting items with lightbulbs next to them, and going to different expeditions/seascapes that have the lightbulbs next to them as well. If you haven't unlocked every area from studying with Balae, do that as well.
It's designed so that you can see all events just by playing through the game normally. The light bulbs go away when you've seen all events that requires that item. If the bulb is still there, you still need more items. Most events require multiple different items. Some events require crafted items from Nicole's lab. There are no plans to list the exact number of items needed for each event because they're just little sprinkles of flavor to break up the monotony at best, and irrelevant to the plot.
