It's all about dps my friend.. Putting enough damage on a boss in a certain amount of time.. Doesn't matter how good are, if you are a low light level then you are doing less damage to enemies that are higher than you.. Take oryx hard for example.. The enemies level appears in red.. Once you reach 311, that goes away and it turns to normal color.. I believe the scale is for every 10 light you are lower than an ememy, you are inflicting 15% less damage than any other person who is higher ranked or even with said enemy.. It's not discrimination, it's about proper execution and damage output to finish a boss off in time. Hope this helps you. Edit- Thank you very much for your service to protect our country.