Step 1: The Materials and Cost
8 - AA 1.2 volt NiMH Rechargeable batteries $6+ (depending on brand)
1 - Eight AA battery clip (4 rows of 2 batteries) $2.50
1 - small piece of aluminum foil a couple cents if you already have some
1 - 3 x 5 notecard a couple cents if you already have some
1 - roll of double sided tape $1.50
1 or 2 - stick(s) of hot glue ~$2 for a small bundle
1 - aluminum heat sink (salvaged, or new) $2-10 (depending on size and seller)
1 - switch or button a couple cents
some wire a couple cents
1 - package of high strength glue (i used JB Weld) $5-8 (this is only necessary if you use the lens
1 - focusing lens large enough for the head of the flashlight (I salvaged this from an overhead
projector, so I am not sure of the price)
Multiple resistors of different values (preferably 1/2 watt), or one 3.9 ohm resistor with a 4-5 watt
1 - small tube of thermal compound grease $1-2
1 - 9v battery clip (optional)
total: roughly $27 depending on what you already have and what brands you buy
(for the batteries, thermal grease, and LED, I suggest ebay. the rechargeables are very cheap, but ive been using them for weeks with no problems yet)
Step 2: The Reflector
take the tape, and cover the note card in rows or tape. then, carefully lay down the aluminum foil (shiny side up) onto the tape and smooth it down. With a pair of scissors, remove the excess aluminum foil from the edges of the card.
on the five inch side of the card, cut halfway though to the other side.
Overlap the two folds of the cut onto each other to make a cone (be sure to have the aluminum foil on the inside of the cone) (the tighter the base of the cone is, the tighter the light beam will be)
with your scissors, cut a hole off the tip of the cone large enough for the entire LED to fit through (just the LED, not the small aluminum heat sink that comes attached to it)
Trace a circle around the inside the note card to create an even guideline for trimming the excess paper.
Step 3: The LED
After doing this, push the LED through the hole in the cone so that the LED itself is on the side with the aluminum showing, but the heat sink that came attached to the LED is on the outside of the cone.
once the leads are wired, add a bit of hot glue to keep the cone pointing straight and connected.
Step 4: The Heat Sink
mount the LED onto the center of the heat sink with a small, evenly spread amount of thermal compound grease. What I did was to spread a small drop onto the aluminum heat sink, the placing the LED on top of it, and swirling the LED in a circle until the grease was evenly distributed.
simply pressing the LED straight down onto the grease doesn't seem to cut it.
Step 5: The Resistors
For this circuit, you will need a 3.9 ohm resistor capable of dissipating 2.2 watts. But to be safe, and to keep the amount of heat generated more widely dispersed, it is best to go with 3-5 watts.
(if you plan on using a different battery voltage (other than the 9.6 volts from the 8 rechargeable batteries, you can calculate the value you will need here: <http://led.linear1.org/1led.wiz> )
I have 13 1/4 watt resistors, which means that the bundle is capable of dissipating 3.25 watts.
I am sorry for the little amount of instruction I can give here, but all I can say is that you need to bundle resistors until you have 3.9 ohms of resistance. Just make sure not to use any that are below 3.9 ohms.
use 12 or more 1/4 watt, 6 or more 1/2 watt, 3 or more 1 watt, 2 or more 2 watt, or if you are lucky enough to find one, 1 or more 3+ watt resistor
Step 6: Assembly
Making sure to have wires soldered onto the positive and negative ends of the LED, use some good glue, such as JB Weld or JB Kwik ( I used JB Weld, and it hasn't failed yet)
Next, secure the reflector cone onto the LED by arching some glue from the edges of the cone to the heat sink as shown in the picture. I highly suggest JB Kwik as it has all the strength of JB weld, but it sets fast enough so that it wont be much of a trouble to wait for it to dry.
Attach the battery clip to the battery holder, and solder the red (positive) wire to the resistor pack with an ON/OFF switch or a button switch somewhere in the middle.
Use a bit of hot glue to attach the resistors onto the battery pack (next to / parallel to the battery clip).
Solder the black wire of the battery clip to the negative lead on the LED (if the black wire reaches that far) or solder it to the wire that is connected to the negative lead on the LED.
Finally, glue the heat sink and LED onto the top of the resistors and battery clip, and glue the switch / button somewhere convenient on the battery pack.
Step 7: Enjoy
Don't forget, if you want the light to be focused as it is shown here in this photo below, try to find some salvaged lens that would fit the reflector cone.
The photo below doesn't give too much credit as to how bright the flashlight is.