I went to a workshop for sewing with conductive thread (it is like regular thread but through magic it conducts electricity, so you can sew a little circuit and light up an LED). We used sets from Kitronic which provides you with some thread, an LED, a battery and battery holder.
I created a lighthouse with felt and then sewed the circuit on the back.
All you do is push the LED through the fabric and open out it’s little legs, then create little loops in the LED legs with pliers. Then attach the battery holder and use the magic thread to connect the positive side of the battery holder with the positive LED leg, and a separate piece of magic thread to connect the negative sides.