How to get digital video camera to not record so grainy? The camera can record in 1080i?

I have a Sony HVR-A1U I bought for shooting interview style clips. I have attempted to play with the settings and am utterly clueless on how to get the picture quality to be comparable to my Sony DCR-200. I was wondering if I had to buy an additional lighting accessory because it is extremely hard to get any clip without grain and the only way I find to take the grainy view off is to lower the exposure.