Wait, 1 sun? So I wont have to put a bunch of lights in places in my map that are pitch black?
Um ... no, you light stuff like real life. That's basically what HDR allows. It is also the varying levels of intensity ... which valve claims to put in an entirely new game play element. Since, if you're in a dark building, for example, and there are windows that get shot out, the bright light will blind you momentarily, it works more like a camera then the human eye though.
The 1 sun comment was because that's how the lost coast is lit. Since, the area doesn't have and electricity. But, yes, it seems they wanted to realistic lighting. They are even talking about how unrealistic lighting in hl2 is currently.
The bad side is HDR takes an arm and a leg to run smoothly! They're suggesting a DX9 card with at least a Gig of ram and 3 Ghz processor (this makes sense, since it's dealing with light calculations!)
I'm really looking forward to the physics processors. Just because, I hope, it works development wise, like the GPU and CPU, since you could use it to process whatever you like, light included!
The other thing that HDR allows, is realistic light bounces. Which means, if there is a large light source ... like a sun ... and that's your only source. The only way an area would be completely black is if it is completely sealed off. But even then, the HDR stuff allows "adjustment" so the cameras eye would adjust to the dark, just like yours. Now, obviously this doesn't matter if it's literally pitch black, since there's no light to enter the eye. But you get the idea.
Valve has said that the goal with the lost coast was to take Source add to it and make it more of a next generation engine. Apparently though ... implimenting HDR, specifically for artists, is going to be more work. Because, skyboxes, for example, have what? 5 different versions depending on intensity.
I think it'll be really nice. Add this with AF, AA, and Depth Feild blurs ... and HL2 would have complete new life breathed into it.
Blame it on Microsoft, God does.