Not much going on here. It's a little clip that sits down between the gaps of wire shelving and you can thread an LED light strip through it. 

The LED light strip shown in the photos is from IKEA.

I've included the Fusion 360 file, in case you'd like to make modifications. Fair warning, though, the variables I configured don't make the most sense, so you might have to fiddle with them a bit to adjust to your needs.

Printing Tips

It probably goes without saying, but I recommend printing these things standing “on their end." The overhangs are generally short enough that you get decent results even without supports.