An easy way is to grind strikes and collect blue l and purple engrams. When you decipher them, do one by one, don't just button smash them all. For example decode one (1) helmet and check the light level. If the current helmet you have equipped is 220 light and the one you just deciphered is 215 you keep the 220 and dismantle the 215. Then you decipher another helmet and this one is 225 equip the 225 and dismantle the 220. Perhaps you're getting them all deciphered all at once and leveling up your light level slower. My cousin was making that mistake and I just wanted to make sure you weren't making the same mistake. I hope that helps, also if you're on ps4 feel free to add me, I spend 65% of the time doing strikes and you're more than welcome to come along. My psn is Akhuma