Introduction: High-powered LED Mag-lite Conversion

This instructable will show how to take an ordinary Mag-lite flashlight and modify it to hold 12--10mm high-powered LEDs. This technique can also be applied to other lights as I will show in future instructables.

Step 1: Tools Needed

Tools Required:

12--10mm High-Powered LEDs (I bought mine from besthongkong on eBay)
Corresponding resistors
Insulated wire (preferably ~20ga)
Soldering Iron
Thin plastic (preferably clear and flexible, I used PETG from a local supplier)
Electrical Tape

Tools Recommended:

Wire stripper
Small pliers
Side-cutting pliers

Step 2: The First Step Is to Modify the Light Bulb

First, take the bulb and CAREFULLY break the glass inside of a bag with a pair of pliers. Using the pliers and soldering iron, empty the bulb casing completely of its contents. Then, using 2 short strands of wire, solder one to the end of the bulb casing and one to the outside casing. When you are sure that the connections are good, fill the bulb casing with glue so as to insulate the connections from accidental shorts.

Step 3: Design and Cut Out the Array

I used AutoCAD to fit as many of the LEDs into an array that would fit inside the Mag-lite. The inside diameter of the Mag's reflector housing is slightly larger than 1.875". It turns out that 12 of these 10mm LEDs will fit. I printed out the pattern making sure to keep the scale 1:1. I printed out 2 of these identical patterns and taped them to the plastic. I drilled one of these in the small holes and the other in the center of the large holes--both with a 1/16th drill bit. I then went back and redrilled the large holes with a 13/32 drill bit. I then cut out the plastic using my scissors, keeping it just barely larger than the outer circle. I then test-fitted the plastic into the Mag-lite housing. It should fit loosely. This would be easier if you have access to a laser cutter, but with a little patience and some skill, you can do a decent enough job without such niceties.

Step 4: Soldering the Array Together

Start by placing all the LEDs through the holes in a uniform manner. I chose to place all the negative leads (flat side) on the outer ring facing outward and facing inward on the inner ring so that all the positive leads can be soldered together. Once the positives are taken care of, attach the resistors to the negative leads. In this example, the LEDs are all wired individually, since the power source is only 4.5V. For flashlights with more voltage, it may be possible to wire the LEDs in pairs, triples, etc. Cut the positive leads and one of the resistor leads to about 3/16" and solder them together. I used a wire stripper to remove pieces of insulation from the wire I had to help insulate the resistor leads from unintentional shorts. The idea here is to wire each LED with its own resistor in parallel to all the other LEDs so that they each receive the same voltage.

I've done some calculations of my own. Since batteries lose voltage over time, I decided I wanted the LEDs to be running at around 95% of their maximum when the batteries were fresh. Here are some resistor values and their corresponding voltages:

These work with the 10mm white LEDs from besthongkong:

volts LEDs ohms
4.5V 1 47
6V 1 120
9V 1 270
9V 2 91

Step 5: Connect the Modified Bulb to the Array

The next step is to solder the modified bulb to the array. Solder the outside of the bulb housing to the negative circuit and the center of the bulb to the positive circuit. Make sure the wires go through the bulb retaining ring so that the bulb housing can be screwed in correctly. Place the plastic form over the LEDs so that they are held straight. The Mag-lite reflector will not be needed, since these LEDs focus the light to a 12 degree spread.

Step 6: Fit the Array Into the Housing

Using the pliers, press the form down hard onto the LEDs. Using the electrical tape, wrap the array with electrical tape until it fits snugly in the flashlight. Press the tape down on the back of the array so that the array will fit correctly in the housing of the flashlight. Now's also a good time to test to see if the array lights up correctly.

Step 7: Make a Spacer Ring

I found that with the reflector removed, the lens no longer fit snugly, and therefore the light would no longer be waterproof. I cut out a thin ring from my plastic to fit. Place the ring on top of the plastic and trace it. Use that to cut a thin ring for a spacer.

Step 8: Put It All Together

Now all that's left to do is put it all together. Make sure the wire stub fits in the narrow, deeper part of the flashlight so that the LED array will sit down nicely. Tighten up all the parts. Now you should have a high-powered, water-resistant, high-strength flashlight for much less than most 'tactical' flashlights.

Step 9: Comparison to Standard Mag-lite

After some feedback, I decided to show how this light compares to the Mag-lite I started with. I've done some calculations from what I could find on the internet and here's the results:

A standard D-cell Alkaline battery contains about 12000 mAh of charge.
Battery Capacity

A 3-cell Mag has 4.5V...this means the whole flashlight has...36000mAh
A 4-cell Mag has 6V--------------------------------------------------------48000mAh
A 6-cell Mag has 9V--------------------------------------------------------72000mAh total

This means that theoretically, with a 1-amp load, a 3-cell should last 45 hours, a 4-cell 48, and a 6-cell 72 hours.

I looked long and hard, and found a site that sells Mag-lite replacement bulbs.
MagLite Replacement Bulbs

Here's an excerpt: (Keep in mind my flashlight is a standard Mag about 8 years old. I'm pretty sure it doesn't have a Krypton bulb.)

MagLite Bulb Type---Base Type---Gas Fill---Batteries---Max Peak Beam---Average---Max Batt
.....................................................................................................Candlepower----Lumens---Life Hours
White Star 3-cell------PR Flange---Krypton---3-C / 3-D---20,000 / 22,000------76.8------4-5 / 9-10
White Star 4-cell------PR Flange---Krypton---4-C / 4-D---24,800 / 23,000-----122.1-----4-5 / 9-10
White Star 6-cell------PR Flange---Krypton---6-C / 6-D---30,100 / 30,000-----162.6-----4-5 / 9-10

So using these Battery life ratings, we can find that:

Flashlight----Volts----Amps----Watts----Assumed Life
3-cell----------4.5V-------3A------13.5W------12 hours
4-cell-----------6V--------4A--------24W-------12 hours
6-cell-----------9V--------6A--------54W-------12 hours

Again, I'm not sure how accurate these numbers are, but from what I could find, these seem reasonable enough.

Using a really cool website I found, the power consumption of these LED arrays can be clearly found. LED series parallel array wizard

For the 3 cell:

4.5-----Source voltage
3.56---diode forward voltage
20-----diode forward current (mA)
12-----number of LEDs in your array

This yields the following information:
  • each 47 ohm resistor dissipates 18.8 mW
  • the wizard thinks 1/4W resistors are fine for your application
  • together, all resistors dissipate 225.6 mW
  • together, the diodes dissipate 854.4 mW
  • total power dissipated by the array is 1080 mW
  • the array draws current of 240 mA from the source.

This means that the whole array puts out 1.08W of power and draws .24A. This is significantly less than any of the bulbs.

As for brightness, see for yourself. These LEDs do not require a reflector because they have a parabolic cross-section which internally focuses each LED individually.

The LEDs I used claim a 12 degree focusing pattern. Not all LEDs do. Many have a 25 degree, while others are as much as 55 degrees. I did a subjective test, and I believe that the pattern is somewhere around 12 degrees. This does mean that across a football field, much of the light would dissipate into a circle 64 feet wide, but at any 'reasonable' distance, the light works great.

As for intensity of light, candlepower is a hard thing to objectively compare, since the overall spread is figured into the equation. First of all, candlepower is no longer a recognized standard unit. It is approximately equal to 1cd or 1 candela. These LEDs advertise a brightness of 130cd apiece x 12 = 1560cd. I'm not sure where the discrepancy is, but after being blinded many times, I know that my roommates can attest to the intensity of this light!

Also, when constructed correctly, the brightness of this light should be the same whether you are using a 3, 4, or 6-cell Mag-lite. The only difference will be overall battery life, which I project to be:

Flashlight----Capacity----Current Draw----Projected Life---Life Compared to Standard 12 Hours
--3-cell-------36000mAh------240mA----------150 hours----------------12.5 times greater
--4-cell-------48000mAh------240mA----------200 hours----------------16.7 times greater
--6-cell-------72000mAh------240mA----------300 hours-----------------25 times greater


ac-dc (author)2007-11-29

There is no need to break the bulb. The contact at the end that touches the batteries can be heated with the iron then quickly shook sideways to fling off the solder, then grasping the bulb the solder point on the side can be melted allowing the whole bulb to slide out whole.

rbormann (author)ac-dc2011-06-26

Ok, but.. what for???

ac-dc (author)rbormann2011-07-21

1) So there is no need to deal with sharp broken glass fragments.

2) When you heat the socket end of the bulb to melt the solder, you're leaving behind a hole to slip the new wire through for more durability so it's a s step you'd take anyway when soldering in the wire... so essentially you are skipping an unnecessary step, there is simply no reason to break the bulb.

Perhaps you should try it both ways to see what I mean.

LinuxH4x0r (author)2007-11-28

I was going to do this with mine, except with red leds (I have tons from a stoplight). I use formica samples and a drill press to make my own boards. it really helps to keep them all pointing the same direction. Nice Instructable!

howboutitbru (author)LinuxH4x0r2007-11-29

leds are in stoplgihts?


LEDs have been in some high level stoplights for about a decade or so. My 1998 VW Golf had a LED high level brake light. They are becoming more common as a general replacement for stop, side and indicator lamps. They certainly are fairly common on newer models of some cars, but they still don't seem to be universal, except in large goods vehicles, where reliability and low maintenance due to the huge MTBF of 100 000 hoursare more important than unit cost and LEDs are now dirt cheap anyway.


No, I meant in traffic signals sort of like this (mine is dialight)


Where did you get it? I'd be interested...


I got mine when mndot (I lived in minnesota all of my life until a few months ago whan I moved to santa fe, NM) changed the lights near my friend's house. (he lives in moundsview, but the lights had a sticker on them that said 65 and bunker hill) I got a working one and one that didn't work so I scrapped it for the leds (~190 of them). I stil have the other one, but it still is in minnesota. The one in the picture isn't mine, mine tas a much rounder standard stoplight look to it. If you want one try DOT auctions or just ask when they are changing the lights.


Thanks! That's actually really close to where I am now at Bethel :)


Thats in Arden hills if I remember right. I lived in shoreview, right next to the mndot place and the (former) ammunition factory. If you are interested in MNDOT auctions they are right next to county rd I and 35W and are usually on saturday mornings.

unclex6 (author)LinuxH4x0r2011-02-26

all most all the lights are leds in Ga.

={) <- man with a mustache


We have had LED traffic signals in the UK for around a decade, but they're still in a minority. Near us some LED signals have been installed and reinstalled repeatedly, and then were replaced with incandescent lamps. I think they may have been problematic. I now get the impression they're becoming more common. It's easy to determine the difference between LEDs and filament lighting, the LEDs are instantly on (visually), whereas the filament lights take time to reach working temperature. (probably around a tenth of a second or so). The LED traffic signals (at least the ones I've seen in the UK all use a matrix of LEDs like those in LinuxH4x0r's picture)


in the US i havent seen a regular light in a stoplight for a while until the other day, it looked way different


I understand that. Some time within the last 10 years, they've started putting LED traffic signals in Minnesota too. I was just wondering where LinuxH4x0r got their hands on one :)

wittzo (author)howboutitbru2008-05-15

We have a few stoplights in town that are LED powered, but the coolest thing we have on the end of my main road at a dangerous intersection is a stop sign that has a bunch of red LED's around it's edge. It has a solar panel that charges a battery for night time. The LED's slowly flash so you can miss the sign. There are tons of intersection warning lights that have solar panels to power their flashing lights so the county didn't have to tap into the main power and get charged by the power company. A guy somewhere in MS invented it, but they're all over the place now.. Cadillac and some higher end European cars started the trend using LED's in their third brakelight, since it's a pain to replace bulbs in. It allows them to make a sleeker light unit, but I've seen few in town that have dead LED's, that's got to be a pain to replace and a nuisance to think that your $XXK car has a 20 cent bulb burned out that will cost $XXX to replace the whole unit...

sivboy (author)2008-04-06

Hey man, Finally got the nerve to get moving on my LED conversion for my 6 C-cell Mag Light. Works great I must say. The only issue I have with it overall is that when putting the housing on, and taking it off, the wires twist together, and sometimes snap, then it's back to the solder gun. I was just showing it to a friend of mine, but now that that's over, I'm not taking the housing off for noone! Appreciate the instructable, and thank you.

GorillazMiko (author)2007-11-27

DANG!!! NICE! freaking awesome, maybe me and a friend will try this, maybe not


Thanks for the enthusiasm!

la3bna (author)MustangChris4292008-02-25

Do you know if this will work on the mag-charger? If it works im def. going to make it

gnasty gnork (author)2008-02-17

I got one of those but it did not include the push button. I have it for about 2 or 3 years. The led part of the unit works perfectly but I don't know about this push button thing but my led thing works fine.

Yerboogieman (author)2007-12-13

what do you mean "night eyes" conversion kits?

Yerboogieman (author)2007-12-10
use this link if you have resistors but dont know they're value

Yerboogieman (author)2007-12-09

now try a mini maglite

omanah (author)2007-12-03

do you have one for sale? i'd be interested, i work at night so this would be of great interest to me.

maxmutant1 (author)2007-12-01

For a LED current limiting resistor calculator
now and in the future, you can get LED resistor values by going to:


i made this sort of maglite hack before but i got one of the biggest like 2 1/2 foot 1s and fit like 14-16 bulbs in

MustangChris429 (author)2007-11-29

Sorry, I would if I had the capability. If you have any ideas for how, I might consider it.


Get pdf creation by downloading it at: www, Rich

triksmada (author)2007-11-30

Great write-up and thoughtful replies. Does anyone know if modified headlights using LED arrays are acceptable to highway use? I had an old 6-volt VW bus that could have used these things.

ac-dc (author)2007-11-29

Batteries in series don't have additive mAH capacity. In any combination there is still only 12K mAH.

Unfortunately from the mag LED spec you list, your LED conversion does not put out as much light as the original bulb did. The reason it looks brighter is because it is blue light in a room with more yellowish ambient light, plus the original maglight was more focused. Regardless, increasing the efficiency, I mean runtime, is still reason enough to do the mod.

Again, the light output is not really 12'. Most of the usable light will be within about 36'.

I roughly estimate your light puts out about 100 lumens, so I was wrong in a previous comment that it's not as bright, it is as bright as some Mag xenon bulbs, but this is only if my estimate does not count light-reducing heat, battery drain which redues current to the LEDs, or LED aging. We can probably ignore the LED aging unless you had a very regular use of the light to put many hours on it, and even then the savings in batteries more than makes up for cost to replace the LEDs at some point.

Check out the website, they have many nice high powered 1-3W LEDs separate or including a reflector set that would drop in to a flashlight and produce more light, more efficiently.

MustangChris429 (author)ac-dc2007-11-29

Whoa...lots of comments. I realize now the mAh capacity doesn't add. Thanks. Also, the light fits within 12 degrees (mostly), but the brightest part is really around 5-10 degrees. I didn't use PCB because this is supposed to be a cheap, easy thing that anyone can do. By my own experimentation, the LEDs throw off WAY less heat than the original bulb did, so I see the heatsinking as a little excessive. Again, this is not supposed to be the ultimate flashlight, but a cheap, easy way to improve the regular old Mag-lite that many people have lying around. Thanks for the tips on where to find more powerful LEDs--if this instructable proves to be as popular as it has been, I might have to check out your lead! Also, the assembly is as waterproof as it originally was, so there is no need to epoxy anything, and the array is held in place simply by doesn't shake around at all.

ac-dc (author)MustangChris4292007-11-29

THe LEDS really do not shine mostly within 12 degrees, see the Besthongkong chart, it is at least +-12' which is 24' minimum but you see on the chart that there is a lot of light left out of that 24' pattern. Yes the LEDs produce less heat but the important thing is they are susceptible to heat when the bulb is not (Much at all). They will get hot and that reduces light. Don't get me wrong that light is nice, and I'm sure if you're like the rest of us you will be building many more lights in the future so I'm just throwing out some ideas.

MustangChris429 (author)ac-dc2007-11-29

Thanks, it seems that you really do know your stuff. What I said comes from my personal [very un-scientific] testing. I just took an estimate of the spread size at a known distance and noticed that it seemed the majority of the light seemed to be at about a 7 or 8 degree spread. Also, it stands to reason that if the 12 degree is the 3dB threshold, there would be significantly more light at 7 degrees than at 12 degrees. Just a thought.

ac-dc (author)2007-11-29

The reflector would be helpful, the LEDs don't actually focus in a 12' beam, that is only the degree measurement of the brightest part, there is still significant light output outside of 12 degrees. However, if the flashlight does not need great distance illumination, many peoploe find a wider than 12' beam more useful for navigation, like inside their home if the power goes out they don't need a tight beam much but rather to see more around them.

mark_gober (author)ac-dc2007-11-29

LED light focus measurements are taken at the points where the power is half it's peak. In other words, they find the brightest point (typically directly in front of the LED) and them move laterally until the power is half as bright. In this instance it would be 6 degrees. 6 degrees for the left and 6 degrees for the right equals twelve degree focus. (Incidentally, these two points are known as the 3db points) So you have half of your overall output in a tight 12 degree pattern and the other half is spread out over the remaining 168 degrees from the base of the led. Needless to say, there is actually very little light outside of the main beam. And most of what is outside is very close to the original 12 degree beam. I'm sure the author can attest to this by merely shifting the beam slightly off center. The intensity rapidly diminishes. This handy for a flashlight though. With traditional LED lights, the tighter the beam, the brighter the intensity of the LED.


That's exactly right...very little light can be seen anywhere except for the 12 degrees straight ahead. Thanks for the knowledgeable insight!

ac-dc (author)MustangChris4292007-11-29

That's because the room is lit. In a pitch black room I have plenty of flashlights using 5mm encapsulated leds with roughly 12' center beam, and while it is much brighter than the rest because of it being centered, if you were to reflect the rest of the light into the center that is spread out along the rest of the axis, you would find there was more light lost than you realize.

MustangChris429 (author)ac-dc2007-11-29

My original attempt was to simply replace the bulb with a single LED, as they are very close to the same size. I found that the intensity of the light changed very little whether or not the reflector was in place, so I just created a great big array with as many of the LEDs as would fit.

ac-dc (author)2007-11-29

The way this has been constructed, it could be nice to take some clear epoxy and entirely cover the back of the LEDs and round frame. This will more rigidly fix them in place but also waterproof the assembly. If a thermal epoxy were used instead of clear, it wouldn't look "as" nice but then the epoxy would help to cool the LEDs more by spreading heat away from the leads.

mark_gober (author)ac-dc2007-11-29

Cool the LED's??? LED's have virtually no heat. They are drawing mere milliamps. (mine draw around 20ma) While I appreciate your attempt to improve the design, that suggestion was a bit off target.

ac-dc (author)mark_gober2007-11-29

Untrue, it is known fact that LEDs both reduce in light output at elevated temp and that they do get hot, because the die is tiny and encapsulated in a relatively poor heat conductor. I can assure you I have made lots of flashlights and when 10 LEDs have their leads short and soldered to a PCB as a 'sink, it does get quite warm, and this across a thermal gradient due to the thin metal leads away from the die (mostly the cathode). If you have a single LED soldered to a fairly beefy piece of wire, this can be effective enoough for a single LED, and at least in the design here it was suggested they ran at 20mA, being easier to keep under a threshold value than 30mA would be (which is closer to the actual spec of these LEDs). Note what I just wrote, since these LEDs are 100mW type and are running at only 20mA, they are not at 100mW, not producing the rated light output. I know this was not directly applicable to what you wrote but it was a good time to mention since it bears on a light output estimation.

mark_gober (author)2007-11-29

Excellent post. Most scary however is that I built a flashlight exactly like yours about a year ago. I even used the same LED supplier that you used. The only difference was that I mounted my LED's into a breadboard and soldered them down. I always get compliments on that light. One other change that I made to mine was to use a piece of neoprene gasket that I cut out with a razor blade to go between the breadboard and the metal case. I have left my flashlight turned on and in a drawer for over 6 weeks and it was still going. You simply can't beat the battery life when you are using LED's. I also have to disagree with spannercrab's comment about switching the batteries to parallel. If you switched the batteries to parallel, you'd get 1.5v, but you'd have 6 times the original mAH. Putting batteries in parallel increases the amount of amps that they can put out over time.

spannercrab (author)2007-11-29

A D-Cell battery does indeed have around 12Ah of charge - depending on type - i.e. alkaline, NiMh etc ... however battery capacity does not increase when cells are strung together in series. 6 x 12,000mAh cells in series will give you 9V @ 12,000mAh - if you strung the same cells together in parallel, this will give you 12,000mAh @ 1.5v (or whatever the single cell voltage is). Also, if you increase the pack voltage, your current drawn through the LED's will also increase and likely destroy your LED's - the only way you can get around this is to either modify the resistors based on your torch voltage or to use a constant current power supply to ensure an even current supply to the LED's.

ac-dc (author)2007-11-29

A large rubber O-ring might also make a nice spacer. However, another option is to take the original reflector and grind down the back of it, then use only the # of LEDs that fit in the then open space. Since the LEDs will (practically) never burn out if not overdriven with too much current, after the lens, remaining portion of the reflector, and LED assembly is installed into the heat, it can be fixed in place with epoxy. Another way to fix the lens in place would be to throughly clean the lens and the ring it seats in, then put a small bead of silicone caulking (or similar) around the inside recess where the lens sits, then put the lens in , wipe off any excess caulking that squirts out the front of the ring, then flip it over on waxed paper and put a weight on the lens (like a D cell battery) until it dries in 24 hours or so.

ac-dc (author)2007-11-29

Why would you make this plastic piece when you could instead use a PCB? The PCB allows drilling holes for only the LED leads allowing better parallel alignment of the LEDs, and if someone is handy at etching their own circuit boards it will be an even more professional result. Even more important, LED brightness and lifespan correspond to temperature, keeping the LEDs cooler by having short leads 'sunk to large copper areas on the PCB will heatsink them. most people don't think about heatsinking LEDs but they aren't trying to put as much current through or don't care as much about brightness as someone building a high performance flashlight might. With several LED running at peak current they will get pretty warm. I think the way this plastic piece was made does look nice though, I am only offering one other alternative.

ac-dc (author)2007-11-29

Instead of lossy resistors, try using an LED driver board for increased efficiency and more constant light output (the way this is set up with resistors, light output continually drops along with battery voltage).

kadris3 (author)2007-11-29

they now have 10mm LEDs which have 5 LEDs in the one case. they are 40 degree with white scatter to 60 degrees. 3.4 forward volts and 100 ma. wicked bright and 265,000 mcd typical,280,000 max. the 5mm 55,000 mcd are also a very bright option fr smaller flashlights. i put one 3mm white bulb in a minimag which worked fine. i had to enlarge the reflector(w an awl) to accept the 3mm bulb. i just cut the leads to the same length as the stock ?krypton bulb. it is not as bright as a minimag bulb, but the batteries last forever. when its dark as a boot it works very well. nice well done instructable.

MustangChris429 (author)2007-11-28

Yeah, it really is much brighter than stock. The light does tend to spread out a little more than a fully-focused stock Mag, but the intensity at the center of the beam is blinding.

smartalx (author)MustangChris4292007-11-29

You don't have any way of measuring your lumen output, do you? It would be interesting to find out how the brightness really compares, you know, with numbers. Also, you are using the standard LEDs. Did you consider using the even brighter Luxeon LEDs? They are more expensive, but FAR brighter. One Luxeon (depending on the wattage) is even brighter than a single Xenon bulb.

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