LED Flashlight with Long Power/Life

The project uses a slightly more complicated circuit to produce a flashlight made from PVC while employing ultra bright LEDs with ballast resistors and extending the battery life by over ten times.

Each LED/resistor combination in this flashlight consumes 4.5V/30mA or around 135mW or power. 25% of power being drained from the batteries is lost in the resistor of each LED chain since the ballast resistor alone consumes 1.1V/30mA or 33mW of power.

In the PVC flashlight the C size batteries have a capacity of about four 500mAh. There is a constant current drain of 210mA or 7×30mA if the flashlight is built with seven LEDs. It becomes obvious that this flashlight will only stay lit for about a day if the seven LEDs are divided into the battery capacity. This is a far cry from the 50-100 hours being claimed by commercial flashlights that runs on smaller AA batteries.

A 23V pulse exist across the series of ultra bright LEDs wherein the human eye cannot distinguish at 278KHz the difference between the pulses and a constantly lit LED which save more battery power. The pulses become apart as the battery voltage decreases.