Choose carefully. I've got two book lights that I've picked up over the years. One I got at Chapters, it's rechargeable and really bright. Too bright for the Kobo. The Kobo may look like print on paper but it is still reflects light more than paper. So the bright light reflects off the front and makes a hot spot that you have to keep tilting to read.
The second on is much dimmer, but it has a goose neck so I can bend it out of the way so that it doesn't shine strait down and reflect back at the eyes. Sort of across from the side which works fairly well.