The one downfall to a Kindle is the fact that the screen doesn't light up itself so you cannot read it in the dark. That's why you are searching for a light for Kindle though am I right? There are a few options here some are quite expensive though so I will have a few different options for you to choose from.
Lighted Leather Cover
This is a nice little product in which you can have a cover to protect your Kindle as well as having a nice slide away light to use just in case you need it. This is a nice light as well, so if you are looking
at the images on Amazon thinking that the light looks like its not getting the whole screen, sorry you are just going to have to trust me that it does in fact get the whole screen just fine. I am a stickler for this kind of stuff so I was worried about that as well.
The only problem with it is that it will run you about $50. That is a considerable investment for me, but well worth it cause the case is so nice, for some though they may just want the light.
Flexible Clip On Light
This is a wonderful solution that is much cheaper, running you about $15. This also isn't a case, it is simply a clip on light with some padding on it. You clip it onto the top right or left corner of your kindle (or if you have another case simply clip it on the case) then turn it on. It does require some adjusting to get the light just right, but like I said I am a stickler for proper lighting.
This is honestly the rout that I would go if you didn't need a case as this is a no fuss solution. Trust me if reading in bed is your goal, then this is the solution.
Simple Light For Kindle
Then there is the best Kindle Light you can get called the SimpleLight. This baby attaches to the keyboard hinge and uses the Kindles battery to power the light. Since it is a simple LED it takes VERY little power yet lights the screen almost perfectly. This has very little draw on the Kindles battery and now there is no need to purchase batteries for your Kindle light. However it comes at a bit more expense, around $23.