The extremely successful Light Stitches projects use a new smart material, Conductive Thread to attach LEDs (lights) to textile projects by simply fastening a knot or sewing onto the LED. This highly conductive thread acts and behaves like conventional thread with the added bonus of being extremely conductive.
Please note that the kits each contain 2x 5mm LEDs except the Rainbow kit, 87-6104, which only contains 1.