So for the beginners out there you may think these items are pretty much useless. WRONG. All of your Strange Coins and Motes of Light should be saved for Xur, Agent of the Nine. He appears on Friday morning (the time depends on your timezone, google it) and vanishes around the same time as he appears on Sunday morning, and he sells one exotic item for each class for 13 Strange Coins, and one exotic engram for 23 Motes of Light which can end up being for any class but you can either bank it or break it down if it's not for your class as high level upgrade materials are pretty valuable at this early stage of your game. Now you're thinking, how do I get more of these?! Simple but not really. They can be earned from strike missions (especially the weekly heroic), crucible, decoding engrams, and public events. These are the known sources. They are also rare to come by.