It’s very simple, you do less damage and take more damage from monsters that are higher level than you. That is why it’s important that you’re at least lvl 28 when doing the raid, since the mobs are lvl 28, you will do less damage to them if you are below lvl 28

Here’s a very simple test I conducted (my guardian is lvl 28):

  1. Buy or obtain white/green/blues so you can change your light level (in this case I had gear where I could change my level to 21, 23, 24, and 28)
  2. Do any story mode at lvl 24 heroic (note, the mobs are lvl 24)
  3. equip your gear so you’re lvl 28, take ONE shot at a mob and note the dmg (383 with a legendary lvl 20 hand cannon in my case to an acolyte)
  4. equip gear so you’re lvl 21, take ONE shot at the same type of mob with the same weapon (I did 184)
  5. equip gear so you’re lvl 23, take ONE shot at the same type of mob with the same weapon (I did 261)
  6. equip gear so you’re lvl 24 (same lvl as the mob) take ONE shot at the same type of mob with the same weapon (I did 383)

Final results doing damage with the same EXACT weapon at the same TYPE OF MOB (lvl 24 acolyte) by just changing my light level

  • Light 21: 184 dmg
  • Light 23: 261 dmg
  • Light 24: 383 dmg
  • Light 26: 383 dmg
  • Light 28: 383 dmg

In Destiny your damage SCALES DOWN TO THAT OF THE ENEMY if you’re higher lvl than it (that’s why your bullet damage text is grey) and you do reduced damage if you’re not the level of your enemy (the same goes for your armor, it scales down to your enemy and you’d take the same damage at lvl 28 as you would lvl 20 from a lvl 4 mob on earth, this is harder to test but trust me, I’ve done some visual tests and confirmed it)


You can only do damage to mobs that are no higher than 3 lvls above you and you take a penalty in damage for it (that’s why you can’t even choose a lvl 28 mission if you’re lower than lvl 25, you wouldn’t do any damage)

  • 4 lvl or lower below mob: 100% damage penalty
  • 3 lvl below mob: ~52% damage penalty
  • 2 lvl below mob: ~42% damage penalty (guesstimate since I didn’t have the gear to put me to lvl 22)
  • 1 lvl below mob: ~32% damage penalty
  • 0 lvl below or higher than mob: 0% damage penalty

Summary:  Your light levels affect BOTH your damage output and how much damage you take only UP TO the level of the mobs (i.e. if you’re lvl 28, you’ll do the same damage and take the same amount of damage from lvl 20 mobs as you would from lvl 24 mobs, there is ZERO difference)


 

via Reddit.