The Blinding Sun was used back when the Brotherhood was forced to keep a low profile. They spent their time studying the Darkness, only carrying out their acts if they are certain they are dealing with a potential host.
One time, the Brotherhood took a Darkness host and raised him as one of their own. As he came of age, the Brotherhood chained him to a table and inserted one of these pears of anguish into his eye sockets. They twisted the pear until it broke the host's forehead and cheekbones.
The relics is found in Jackie's mansions dining room near the kitchen, during Brotherhood's assault on it.