Professional Slides presentations. Light or dark background?

I must choose my company's default PowerPoint presentation template.

Having in mind that this template should be versatile, and that people want to create presentations quickly, should I create a template with light or dark background? Which is more usable.

I must say I'm inclined to light, because it might be easier to read black text and because it is easier to use with white background images (no Sales guy will look for an image with transparent background, that's for sure. I've seen very ugly stuff). But, are there any cons to using a light background? Please help me.

Note: I'm talking about day-to-day presentations. Not a presentation for a conference that would take you 20+ hours to prepare.