You can always buy a pre-made one for $14 but if you're a DIY'er, I rather spend $0.50 cents and have fun doing it. Yes, buying 20 pieces of bead emitters will cost you from $3+ to $5+ but having several extras, you'll have several creative uses for it. Like: I converted a $2 Harbor Freight incandescent head light to LED. And I re-purposed a quarts light by stringing 4 LED's in series on an aluminum plate and using a 12v 1a power plug laying around as power . (I think those 4 D cell MAG LITE uses the same type of bulb.)
I made two of these bulbs already and used them for a few months now. It is a lot brighter than the original bulb and happy with the results. That is why I like to share it. The only imperfection is that when it shines, it has a wide spread with a hole in the middle. This is how the lens was built and designed for incandescent bulb. Like the title said, "simple"! If you think you have a better idea, share it!
For this flashlight bulb mod, I intended to hack my old four AA (4 - 1.5v in series) 6v flashlight. I used 3.9 ohm resistor for this DIY, (I used this calculator: http://led.linear1.org/1led.wiz). For flashlight bulb with two cells, no need to put any resistor but you still need a heatsink (HF head light).
PARTS YOU NEED:
1) Type L Mechanical Connector, split bolt, or any thing similar (I just used that because I have it in my scrap drawer).
a. The main thing is that the diameter fits the base of the bulb and the top should be flat to mount the emitter,
b. It must be aluminum or copper to act a heatsink (to absorb the heat from the LED emitter)
c. Must have a hole in the bottom and on the side for the positive wiring.
2) Alcohol (for cleaning)
3) Incandescent flashlight bulb
5) soldering gun and lead
6) Arctic silver alumina epoxy
7) 1w or 3w LED bead emitter (I used cool white 170-190Lm 6000K)
They are available at Amazon (from $3+ up to $5 for 20 pcs). You can search for "1W or 3W White LED Bead Emitters"
8) A piece of wire, spliced just to get the plastic insulator.
9) Optional: Any plastic with 1/8" hole and a small clamp (I cut about 1/4" of a plastic wall anchor with 1/8" hole) I used this to protect the lens of the bead emitter which is 1/8" diameter.
Hacksaw, pliers, needle nose pliers, metal file, drill or dremel the smallest diameter bit (1/16"), and safety glasses
Step 1: Prepare the Parts Needed
1. Using pliers, crack/break the glass part of the bulb (pointing towards the garbage can), and carefully clean all the inside of the bulb.
2. using a hacksaw cut the tab of the mechanical connector and use metal file to round it off. You just created your copper heatsink.
3. using a dremel or a drill, carefully drill the bottom center of the bulb. Note: the black part of the insulation in the bottom of the bulb is very brittle (I broke my first attempt that I need to superglue it back).
Step 2: Assembly
a) insert the a little piece of plastic wire insulator (about 1/4", extracted from any electrical wire) in the resistor then thru the 1/16" hole.
b) I used the foam in my soldering base to hold it in place. Then, solder the wire from the resistor on the bottom of the bulb. Cut the rest of the resistor lead plush to the bottom of the bulb.
b) insert another piece of plastic wire insulator to the top area of the resistor, thru the hole in the side of the copper heatsink. Then, solder the heatsink to the base of the bulb.
c) If you will use a clamp and plastic spacer, this is the time to check if it will fit the bulb and emitter. Using alcohol, clean both the top of the heatsink and the bottom of the bead emitter. then, let it dry. Mix just a little bit of the Arctic Silver epoxy. Just a dot of each part A & B. Attach the emitter making sure the positive side is facing the positive side with the insulation. Let it dry overnight.
d) With a needle nose pliers bend the positive and negative plate of emitter to 90 degrees pointing downwards. trim the resistor leads/insulation and solder it to the positive plate of emitter (making sure it is well insulated and not touching any metal surface). I just used the cut piece wire of the resistor and solder it to the negative side of the bulb (which is any metal part of the base of the bulb).