So the TWAB says that bright engrams will be "heavily weighted" to not give duplicates. But the thing is, anything that you can get duplicates of can also be pulled from the collections, so a bright engram with a duplicate is just a disappointment. It's worth less than nothing, I used to be excited to see what comes from a bright engram, now I open it with no anticipation at all. I'm not a game designer, but it's probably a good idea to minimise the times that a reward makes a player think (or notice, depending on your outlook) they've wasted their time.