Sometimes in high-contrast conditions, a white line appears in the viewfinder. I have seen this when I set the ISO setting high, typically when the overall lighting conditions are very dark. To me, the line looks like `crawling ants'.
Tels (dpreview, Panasonic forum, 11 March 2004) explains...
> I see this occasionally when viewing an image that is really bright like the sun, but otherwise no.
The reason is that the pixels in the CCD are stored and read-out in rows, so if some pixels in one row get too much light, they overflow (really, the electrons overflow due too much photons hitting the pixel) into the neighbour pixels. The final photo does not show it, because it is used with a short shutter time, while the LCD lifeview has basically the shutter open all the time.
The white line(s) are no problem thus, just an artefact from the working of the CCD chip.
Now, if you get a white/bright line in the exact center, and it is also visible on the final image, you got a problem. Someone had this, I remember, and his camera had to be swapped by panasonic.
(btw, the first effect is why you also see the overflow in video: there the shutter is open quite alof of time (of not always) and thus this happens. single pictures don't have the problem, as long as the camera can select a short-enough shutter -- but basically with 1/2000 second even direct sun photos work out ok).To re-iterate, if the `white line' appears in your final image as well, then your camera is defective. Get a replacement!