Draw Settings - Iray Interactive scene mostly black?

FirePro9

I generally set the Draw Settings | Draw Mode to Interactive when using Iray in the viewport in order to speed up screen redraws, however, with this new product SC20 Botanical Garden the viewport is mostly black, though if I turn on the camera headlamp it helps quite a bit.  If I change the Draw Mode to Photoreal the viewport is good.  Is this an issue with certain products or is this a common problem or am I misunderstanding how Interactive mode is suppose to work?  Thanks!