Optic

You have a choice; three beam angles are available, narrow, medium and wide. I’d recommend the medium for general use or the narrow for a longer throw of light.

Resistors

I have used 0.6W resistors, you will see from the design calculations (figure 2), the power dissipated in the main beam resistor is more than 0.6W; hence, to achieve the 3.4Ω required I have used 2x 6.8Ω resistors in parallel, thus doubling the power rating to 1.2W.

Batteries

The higher the battery capacity the longer the light will last. The parts list calls up 2.7AH NiMH cells; 2.7AH is currently the highest available capacity in AA size.

Non rechargeable alkaline batteries can be used. They have a higher initial voltage of 1.5V per cell compared with 1.2V for NiMH. The 3.4Ω resistor value chosen ensure the LED will not be damaged by this higher voltage. The voltage output of alkaline cells is much less constant than for NiMH, the voltage will drop continually as the battery discharges, thus the light output, although initially brighter with the alkaline batteries, will fall off as the batteries discharge. The overall useful life for good quality Duracell or Energizer batteries, will be similar to that with NiMH batteries.

The design is capable from working on voltages between 3.6V and ~6V; hence, it is compatible with Speleo Technics Headlight batteries, FX3 and FX5 batteries, along with Kirby Kidney packs and Oldhams Batteries.

At 3.6V the light output will be much lower, and a lower value of resistor will be required to give a useable light.

At 6V the light output will be brighter, though with the proposed 3.4Ω resistor the LED current is still within the LEDs range.

Note: the efficiency decreases with higher voltages; hence, a higher voltage with similar capacity will not give a longer life.