In a surprise move, Nintendo recently (and quietly) released an updated version of its Game Boy Advance-SP. This new version of the hardware originally released in March of 2003 is exactly like the GBA-SP that you're used to. The only difference is that the new model has a fully backlit screen instead of the standard front lighting. And, if you though that the SP looked bright before, wait until you see it now.
The SP's light button, that previously turned the system's screen lights on and off, now toggles between two different brightness levels for the backlit screen. The default "low light" setting is noticeably brighter than the old SP screen, and when you turn the brightest level up, you'll be stunned at just how dark the original SP appears.