Your lighting will depend on two things: getting the proper heat gradient and getting the proper kinds of light.
Your first challenge is that a 20 gallon tank is extremely hard to manage proper temperatures. You will for sure need to get a digital thermometer (any garden center for about $10-$15) as the little round thermometers and the stick on kind are about as useful as guessing - they can be up to 20 degrees off, which is dangerous.
The basking temps should be around 120F (a little less if your new uro is little bitty). Air temps on the rest of the warm side should be around 100F and the cool side around 80F. Whatever kind of bulb you need to get those temps are what you need - regular household lights, reptile basking lights, whatever. The kind isn't important, just the temperatures are.
Next part is the UVB (keep in mind some people say you don't need UVB if you supplement with vitamin D3 - that's possible, jury's still out, but I prefer to play it safe and provide UVB). In a tank that small your only option is a UVB fluorescent. The best ones are Reptisun 5.0 - tried and true and very reliable. The bulb can't be blocked with a plastic cover and the UVB will be reduced (though not eliminated) if the light shines through a screen tank lid. The closer the lizard can get to the tube, the better (up to about 6"
. Over about 12" away, there's no real UVB reaching the lizard.
Sufficient UVA should be there already as long as you have the other bits covered.
If you have the space, a dual fluorescent is a great idea - you can add either a second UVB tube or a "full spectrum" (no UVB, but excellent visible light) tube, but I don't think you can get that with a 20 gallon tank.
I hope that answers your question - please feel free to ask for clarification if I made a mess of it. Here's a picture of one of my tanks so you can see how I have it set up. Fluorescent fixture along the back, with heat lights in the domes. I have a different UVB bulb, but the setup still looks similar. My fluorescent is WAY too far away to provide UVB if I was using that kind of bulb so keep that in mind, too. 
You can also look over all the wonderful care sheets here on Kingsnake (Care sheet link at top of page) or visit Deer Fern Farms for additional information that will help you out a lot with your new uro. Congratulations! Uros are great pets!!
Tell us more about your new guy? Name? Species? Size? And pictures are required. 

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Torey
Eugene, Oregon, USA
1.1 Uromastyx geyri (Joe and Arthur)
3.0 Uromastyx dispar maliensis (Tank, Turtle, and Spike)
1.0 Uromastyx ornata (Scuttlebutt)
2.1 Anolis carolinensis (Bowser, Sprocket, and Leeloo)
0.1 African dwarf frog (Sheila)
1.0 Betta splendens (Mr. Miagi)
1.1 Felis domesticus (Roscolux and Jenny)
