Economy high brightness led flashlight circuit

A very simple economy high brightness led flashlight circuit can be made using a simple AC-DC converter from some other unused device like an mobile phone, and some common resistors and high brightness leds.
This high brightness led flashlight circuit use 30 warm white leds connected like in the figure bellow . This circuit use is powered from a 7.8 dc power supply , so I used a 100 ohms resistor in series with each row ( 2 leds x15 rows).
You can use a small value resistor to design your circuit for a high forward voltage, but in this case you need to route just one side of the pcb or maybe a small heatsink because these leds will become very hot.