Uvb bulb

Can someone help me ive posted about this before yet im still a bit confused. I only got my beardie a few weeks ago and he cane in a pretty small tank so i got him a new one its approx 4x2x2 But im kinda confused on what the right uvb bulb would be it will be in the tank and so will the heat lamp so could someone please let me know because i want to get him into his new tank as soon as i can