The light level is the deciding factor in the MMO shooter Destiny. With this, Bungie directs the progression and makes it extremely difficult for low-level players to survive in higher content.
Meta stat light level in Destiny is crucial
Actually, one would think in an MMO that you should be as strong as the gear you wear, as the stats on it suggest. But apparently, that’s not quite the case in Destiny.
The light level, a meta stat that was previously believed to only show how strong you are, does more than just that. It ultimately determines how strong you are. Because the light level proves to be the probably most important factor. It decides how much damage the Guardian does to higher-level mobs.
A user on reddit has now discovered this in a self-test. He changed his gear so that he sank below the level of an opponent and then controlled his damage output. What came out can only be explained by the unexpectedly central role that the light level plays in damage calculation.
Here are his results:
• 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

If the numbers are correct, and that seems likely, it means: Bungie wants players in Destiny to tackle the content linearly and ensures with this trick that everyone adheres to it and stays in their weight class, lest they feel like they have a pea shooter in hand.
Important for you: If you have been frustrated that you replaced one item with another, although it is worse in every respect except for the light level, you can now have a clear conscience: it is indeed an upgrade.
The redditor interprets his results that it is crucial to reach a light level of 28 for the raids to deal full damage to the mobs.
Tips on increasing the light level in Destiny can be found here. In the currently ongoing event “Queen’s Wrath,” you can stock up on legendary items.