This ultra-thin bookmark folds to become a reading light
Created by Japanese product design firm Kyouei Design, the bookmark uses special ink that conducts electricity.
That ink is printed in the pattern of a simple circuit - in a flat state, the bookmark is just an open circuit. But when you place a battery on one end and connect the positive and negative sides of the bookmark to the corresponding sides of the battery, you close the circuit. That allows electricity to flow to two LED lights that are built into the middle of the two-dimensional circuit.
The bookmark requires a CR2032 watch battery, which is sold separately. Unfortunately, you need to hold the battery in between the two sides of the bookmark to keep the circuit closed, so you might need tape handy if you want a hands-free solution.
The bookmark can be ordered from DesignBoom for $16, or purchased from one of Kyouei's international distributors.