If you’ve got the Destiny 2: Curse of Osiris DLC then you’ll have already been to the lighthouse on Mercury to see Brother Vance. But I bet you didn't know that there's also a chest trapped behind a forcefield here that you’ll want to open.
Upon entering the lighthouse head towards the platform Brother vance is standing on and, once there, look at the desk to his left and you’ll see and glowing book. Activate it and you’ll start the sequence. Immediately turn around 180 degrees and head over to the far wall. You’ll see three fire pits and to the left of the centre one is another book. Activate this then head right around the outer ring.
Head past the entrance steps and when you go past the next fire pit look left to find another book to activate. Examine this ‘aged book’ and head all the way back the way you came along the outer ring of the room until you reach the long table on your left, near the end of the table you’ll find another book. Activate this and head back in the opposite direction past the entrance portal again. Now keep going past the stone door and jump up onto the first bookshelf you come to on the left. Examine this book and you’ll see a ‘Decryption conflux activated message’ in the lower left. Now go back towards the long table from earlier and you’ll see the conflux close to a pillar. Run over to this and interact with it to get a ‘firewall decrypted message’
Finally head back to the entrance portal platform, drop down the other side and turn around to find the chest. Open it for your reward.
Quick note: The firewall will be lowered for everyone in the space until the timer runs out so if you’re lucky someone will have done all the hard work for you but if not it shouldn't take you long now you have this guide.