Step 1: Material
1x 1 meter of 12mm copper pipe
2x 12mm copper end caps
1x Cree XLamp XR-E-B3 465nm-470nm Blue LED (XREBLU-L1-0000-00K01) presoldered onto a 20mm PCB board
(Note: the 16mm PCB board might fit better on the end cap but will be more difficult to solder onto the endcap because of its smaller size)
1x 1 Ohm resistor rated above 1W
1x Suitable power supply (DC 3.3-3.7V@1A)
Warning: If you use a USB 3.0 port. Make sure the port can handle more than 1A. Some Gigabyte motherboards have 3x-USB-power. On its USB-3 ports this means 3 x 900mA = 2700mA.