This is my first beardie so I’m still learning. He’s about 2 months old. His setup is a ZooMed starter kit. I know somethings they put in those kits aren’t exactly the best equipment. It’s a 20 gallon tank with the basic 75 watt basking bulb. I threw out the calcium that came with the kit since it was without D3. He has one of those double lamp sockets. Do the lights need to be seperated?
I would definitely upgrade the lighting. For a 20g setup I'd probably pick up a T5 5.0 UVB light like this https://www.amazon.com/Zoo-Med-26053-Reptisun-Terrarium/dp/B00AQU8F2O and then just put it on top. When you get a larger tank you should upgrade the bulb to a 10.0 or an Arcadia 12%. I also suggest getting a couple of digital thermometers with probes. Put one in the basking area and one on the cool side right on the surface so you can see what the temperature gradient is. You want the basking surface to be between about 100-110 and the cool side should be between about 75-85 or so. You can put the basking light on an adjustable stand and change the height to adjust the temps. You can also change the wattage of the bulb as needed.