I didn't know a tool like this existed. Maybe it's not weird since I'm no electrician, and I don't know anyone who is. As I've mentioned earlier, I've bought some Philips Hue lamps, and I have more lights on my wishlist. Therefore my dad suggested that I should buy a tool that could strip the wire. My parents also want Philips Hue lights, and with a wire stripper, the work is a lot easier.
My dad and I started hunting for a wire stripper, but it's not easy to know what to look for when you don't have any experience in the area. We searched the internet, including Amazon, and spend some time reading reviews.
We ended up buying a wire stripper from Knipex, which is automatic. That is, you put the wire in the 'mouth' of the wire stripper and squeeze - and the insulation is gone. I've tested it on some wire, and it works. I look forward to using it next time I have to put up a light.