I wanted a ring light I could use for video with my iPhone and camera. I didn't understand the ballast thing for a while, but then, I realized that each ballast tells you what model number of light tube to use. So, I found the light tubes I wanted, then searched for the ballast that would work.
I saw tutorials for making LED ring lights and they seemed really complicated. This one isn't complicated, but it wasn't as simple as it could have been - e.g. if I used a shiny tray instead of an oil drip pan and foil tape, that would have removed a step. I probably could have gotten some proper hardware for mounting to the tripod (or light stand) also, then I wouldn't have needed to make that wooden thing.
I think the only thing you can't see in the photos below is that I put washers around two wood screws and screwed through the pan into the wooden cross to connect them.
I use a camera behind the ring and an iPhone in front of the ring.
12in Light Tube8in Light TubeFluorescent BallastPlug Thing
Plus this stuff
dollar store aluminum foil tape
dollar store oil pan
old duct tape roll
1/4"-20 insert nut (for mounting it to a tripod) (home depot)
matte black paint
screws (dollar store)
washers (dollar store)
Mounted on a tripod with camera behind mounted on another tripod
My JOBY phone holder wedges into the tube pretty nicely when an iPhone 5s is in it with case.
That's how I took this photo.