Yes, UVB everyday is just as important as the basking lamp. The UVB bulbs only put a fraction of the light out that the sun does, so it's important to always provide UVB for the long term health of indoor chameleons.
UVB is vital for the absorption of calcium and vitamin D. You chameleon should have the UVB light on every day for 12-14 hours a day. Less UVB can cause serious health complications like Metabolic Bone Disease (MBD)
As Lathis said, a brand new UVB puts out only a fraction of the amount the sun does. Plus it doesn't go very far from the bulb. Your bulb is further compromised by the screen between it and the cage.