Since I started playing NV again after the last patch, certain things (special graphics effects, it turns out) being within my frontal line of sight (even at extremely long distances from me) are causing this awful puke-yellow strobing affect on my screen, which makes the screen painfully unusable until you turn your head/view away to the sides, to where the cause of the strobing is no longer in your frontal zone. But as soon as you look back in the direction it came from, it starts up again.

So, I gritted my teeth and went straight towards the cause of the strobing, and the first cause I identified was the hazy, propane-flame-like exhaust that is discharged underneath Mr. Gutsy robots. As soon as I kill the robot and the emissions stop, the strobing goes away. Since then, I have identified several other causes of this affect, including enemies that are actively using stealth boys (again, a hazy, ephemeral kind of special effect), such as the Nightkin; and the greenish explosions from pulse grenades or the Meltdown explosion affect. It's only these hazy, amorphous kinds of special affects that cause the strobing on my screen.

I updated the drivers on my ATI Radeon 5870 card recently, so I'm sure it's not old drivers. Any thoughts or ideas?

Well, I figured it out... in the game settings, under 'screen effects', there are three choices- none, bloom, and HDR. It was set to none, and when I switched it to HDR, the horrible strobing affect disappeared. Can anyone tell me what the HDR option is about?

I also have this issue with Radeon 4870HD. Nightkin in New Vegas and Mr. Gutsy in Fallout 3. Very distracting. HDR is short for "High Dynamic Range" The actual implementation is very technical but I think it has to do with the light sources ability to change colors based on time of day - based on what Valve said they used it for in HL2 (orangecasting the light sources to emulate sunset conditions). I'm not sure why the lack of HDR would mess up the stealth boy cloak effect. Thanks for diagnosing this, I'll turn HDR back on in both of my Fallouts.