In which a noob asks a lighting question

thricesk

Hi, I've just started tinkering with DAZ and am having an issue with lighting.  I've uploaded a small (400kb) scene file here to demonstrate the problem.

The scene is a simple, but very large (100m) room with four walls and a ceiling, and one point light 50m up.  It looks correct in the viewport in Iray preview mode:

But in texture shaded mode, it looks like this:

How can I fix this scene so I can work with it in texture shaded?

I know I can hit CTRL+L to turn on a camera headlight, but that doesn't work too well since everything in the actual scene I'm working on is still quite dark.

After tinkering, I've discovered that I can fix the problem by going into every object shader and assigning it a white Emission Color, but is that going to be practical later on?  Does Emission Color actually do anything if the accompanying slider is set to 0?

Edit: typo