The only source 3 Light level gear is the gear you get from Spectral packages. As of the release of Rise of Iron, the only way to obtain a Spectral package is by completing the Level 41 Prison of Elders. This can be done once per week per account.
Prior to the release of Rise of Iron, there were three ways to get Spectral packages for free:
- From the Postmaster
- Completing the Level 41 Prison of Elders
- Finishing a game in the weekly featured Crucible Playlist
You could also buy Spectral packages for Silver prior to Rise of Iron. Silver can be bought from Xbox Live / PSN for real money.
The reason that they only provide 3 Light is because they can be bought for real world money. In order for them to be usable, you will need to infuse them with gear you got from playing the game. This is to prevent "pay to win".