My gooseneck lamp from IKEA to illuminate the inside of a guitar broke. I did some searching online and found a better solution with a small USB spotlight and one USB charger purchased from Swedish Amazon. A simple modification with a rubber and steel washer (which was screwed into a sandwich) allowed me to attach the spotlight to the side with a super magnet from the outside and also direct the light where I want as the spotlight can be adjusted. I drilled and tapped two holes for metal screws in the washer and cut the screws flush with the surface of the washer. The cord, which has two thin wires at the very end that can easily break, is clamped by the metal and rubber washers with two screws. 

Demonstrating the spotlight on a guitar that has not yet had the bottom glued back on.

Here it is for real inside a Levin 1906. It works great, it doesn't get in the way inside, gives a stable light that you can place it wherever you want.

Edit: I have now tested it a number of times and it is fantastic! Completely superior to any other way of illuminating the inside of a guitar that I have tested. One last detail is that I protect the lacquer on the outside of the sides by taping a cut-out round piece of duct tape on both sides of the magnet