Remember the light pens you used to be able to get that let you draw on your computer screen (I’m talking ZX Spectrum time here). They were of dubious usefulness to say the least. However this light pen, the LED Moonlight is much more useful.
The LED Moonlight pen has all the features of a conventional pen (i.e. it can write on paper) but also includes a light so that you can write in the dark (and be able to read it afterwards). I always carry a notebook with me as I never know when I’ll have the next (or should that be first) great idea, though when in bed turning the light on to do a quick scribble about my next website idea would result in a sharp dig in the back. However with this pen I could scribble away with out fear of reprisal.
You can get the LED Moonlight Pen from Latest Buy for ~£5.