Trusted Reviews take a look at the Nintendo DS Lite - Handheld Console. Here's a bit:

But the DS Lite's beauty is far from skin deep. As I already mentioned, the dual screens in the original DS were pretty lacklustre, but Nintendo has addressed this issue. Not only are the screens far brighter in the DS Lite, but they look subjectively sharper, while the viewing angle is light years ahead of the older displays. The touch screen is especially impressive, considering how dull it was before, while the improvement in viewing angle is nothing short of staggering - the picture below shows how the touch screen looks like it's switched off on the old DS.

You can set four levels of brightness for the screens, with level one being roughly equivalent to the original DS. Obviously the screen brightness has an effect on battery life, but even with the brightness set to maximum, you're still looking at around eight hours of play time - that's more than double what you could expect from a PSP. To be honest I actually found the top setting too bright, and was very happy with level three, or even two, so I'll probably be looking at well over 10 hours battery life - that's level three in the picture.