I have one, they do not drain sufficient power to result in power loss at the keyboard, or from your laptop. They come in various configurations, however, none of the gooseneck models that I know of are longer than about 12 inches. There are some, however, that are clip-on and have about 18 inches of wire between the USB plug and the clip-on light.
As for lighting the entire top of the keyboard, probably not sufficient unless it's a really dark situation. Much better off going to Lowes and purchasing a 20-inch LED strip light for about $25, or the same size incandescent strip light for $14. Lots of soft, even light that can be directed where you need it. Some of the strip lights come with an adhesive mounting strip, while others have tiny screwes that are used with mounting caps.
Cheers,
Gary
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Travlin' Easy
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)