I believe the floodlight is the best option other than afterburner.
However, it eats up batteries fast, makes it really heavy, and much larger. On top of all that, it doesn't do all that great of a job.. theres no way you can play it in the complete darkness still.
Do yourself a favor and buy the Gameboy Advance SP. Trust me, the light is worth the price difference alone. I don't know about everyone else, but I play with the light on 99% of the time as it still makes some visible difference no matter the lighting conditions.