Cold end experiment

So I decided to try and build a cold end out of recycled printer parts and readily available stuff. I came up with a build that looks a lot like other minimalistic designs. I also wrote a sketch with My arduino for a LED that is mounted on the cold end. The brighter the LED , the hotter the hot end is. It won't tell me exact temperature, but all I need is a basic idea.
The order got messed up but you get the idea. The brighter the hotter.