Introduction to modifying flashlights ...


Well-known member
Jan 10, 2005
Texas, USA, Earth
Members of another non-flashlight related forum asked me late last year to put together a basic introduction to modifying flashlights, so I put together this two part intro that I show below. Many folks here in the forum know a lot more and have more experience than I do, so just keep in mind that this was meant as a place to start, and not to be the most up to date "ultimate" guide.

I will do my best to update/correct this as needed. I hope this is somewhat helpful to at least a few of you.

Last edited:


Well-known member
Jan 10, 2005
Texas, USA, Earth
Re: Introduction to modyfing flashlights ...

Modifying flashlights - Part 1

by William Quiles

December 2009

Modifying a flashlight is something that can be rewarding, fun, practical, challenging, and even dangerous; covering very small lights using a single 5mm LED (Light Emitting Diode), all the way to multiple high power LED's (or very high power incandescent bulbs) to create multi thousand lumen “torches”. Although there are plenty of cheap, reasonable priced, and expensive off-the-shelf lights available to suit every need imaginable, there is something unique about modifying something and making in your own – something that brings you pride when you can answer: “yes, I did that myself!”.

I have been modifying flashlights for myself and others for about 5 years now (since late 2004), so I have of course developed some preferences along the way, which of course bias my point of view, and the recommendations I would give somebody else. I am a beginner machinist with a lathe, mill, and band saw, and I also have a full electronics bench as I am also an Engineer (BSEE and MSEE), so I perhaps have a different take on things, which will of course bias how I look at any project, be it on machining, electronics, flashlights, etc.., so please keep that in mind as you read this. You can see a list of most of my projects here at the CandlePowerForums, which is a great site to learn/share everything/anything about flashlights, illumination, technology, etc.:

The goals in modifying flashlights are immensely varied, but “most” of the time it involves simply making a given light/host brighter than “normal”, sometimes pushing the envelope with whatever is considered state of the art at the moment. I say at the moment, because the whole ecosystem of suppliers, manufacturers, modders, etc., never rest – there is always a brighter bulb or LED in the horizon, some denser more efficient (and/or safer) battery chemistry to be used, or some new exotic material to be used (Titanium is quite popular today). A light that you modify today and that is considered “cool” right now, will likely be a “so so” light in as little as 4-6 months from now, so the so called “flashaholic” will keep buying, selling, upgrading, modifying as part of this never ending hobby.

Here are a couple of LED mods on perhaps the most common hosts available - the Maglite hosts (in both C and D size):






Some modifications tent to border on the impractical – far too bright, far too short runtime, too big/heavy/cumbersome, or intense heat so great that you would not hold it with your bare hands longer than 5 minutes or risk burning your skin and/or permanently damaging the light itself (self-destruct). On the other hand, some modifications tend to be more practical, like making modest increases in output, giving a light longer runtime, changing to a different battery chemistry (rechargeable), of changing the type/shape of the output beam.

Using a diving-rated host, I made this version which borders on the impractical (host is second left to right on first picture):



Here is a simple example of a fairly simple and "practical" mod - turning a DeWalt 18V Light into an LED light for long runtimes and close-up work:


Modifying flashlights can be grouped in many ways, but to keep things simple, I am going to talk about two large categories: incandescent lights and LED lights. There are a few hybrid lights that incorporate both, my travel EDC (Every Day Cary) SureFire A2 comes to mind, but for the most part flashlights either use a hot wire (filament) to make light, or a LED to make light.

Size is the other significant way to separate flashlights – not only the size of the host, but also of the batteries that power them. In the end, a flashlight is nothing more than a container of cells/batteries which store the energy to be converted into practical (or non practical!) illumination. Unfortunately as you will see, it is this “container” and the quantity/type of cells that fit in that container, what determines and dictates a “lot” about what can be modified and how. There are exceptions, specifically canister diving lights were the “head” and the battery are separate, but those builds are a little bit more involved given the nature of the environment in which they will be used.

The C and D Maglites are what I consider the larger size for modification. Of course, one of my specialties is to turn a regular C or D into a single cell version (a 1xC or 1xD) to use with various small form factor battery adapters. From top: "C" cell, FM 4xAA holder, WQ's custom 18650 LiIon holder, FM's 4x14670 holder:

Here on the left is a 1xD next to a 1xC:


Of course I do all of the machining and re-threading myself:




Host wise,from left to right: OEM Dark Silver (Pewter) 2xC, WQ 1xD Copper, WQ 1xD Black, OEM 2xD Black, OEM 3xD Digital Camo, OEM 3xD Purple, OEM 4xD Copper, OEM 6xD Black:


This is an example of a smaller light: it uses 2x CR123 cells, or a single 17670 LiIon cell (depending on the LED module):


Incandescent lights:

These lights use a filament that when heated by the flowing current in a sealed glass envelope it transforms part of that as heat and part in the visible spectrum. The more current flows through the filament, the brighter and whiter the beam becomes, but the life of the bulb also decreases, so there is always a compromise to be made. It should be noted that most incandescent bubs are slightly (or quite) under-driven, which is why they look very yellowish in color, instead of a beautiful white color, so when I talk about incandescent bulbs, I am only refering to "properly" driven ones.

Bulbs are voltage controlled devices - you get a constant output when the voltage is keep constant, so if using a regulator, one would use a voltage regulator. Bulbs have a "rated" voltage, but you can typically exceed this value, if willing to make the sacrifice of a shorter life for the bulb, but care must be had when over-driving a bulb since if the voltage is too high, the filament will melt and that would be the permanent end for that bulb.

The other significant challenge that bulbs face, is that when the filament is cold (it has not been used in a while) its resistance to current is much lower than once in operation, so it suffers from a current spike when voltage is first applied. This is the reason most bulbs in the home die after a while - and they don't die while they are ON, they die when you first turn them ON. If a bulb is operated in its "normal" envelope/range, the chance of dying (melting the wire) is not as great, but as the bulb is overdriven more and more, the chances of this over-current situation increase dramatically.

One of the most exciting developments is the availability of circuits that implement a "soft start" by where the voltage is not applied in full during the first couple hundred miliseconds, but rather it is increased slowly. Mind you it happens pretty fast (less than 1/2 second), but that is all that is needed to prevent the bulb from dying. In addition to soft start capability, some of the newer drivers available today offer also regulation: these drivers take a high voltage (too high for the bulb) and using Pulse-Width-Modulation (PWM) they develop and maintain an "average" DC voltage as the batteries drain - this is the best driver to buy, and since the switching element (FET) is being switched very fast, these designs are also extremely efficient at 98-99% efficient. Here you can see a soft-start circuit in operation, as well as the PWM taking place:


Due to the filament radiating energy in a relatively larger spectrum than most LED's, bulbs tend to have a more "natural" look - they seem more like sunlight. Being that this is very subjective, opinions vary a lot, but to me the best incandescent bulbs still look better than the best "warm" LED's (more on this below). Here is a comparison at night between a well driven bulb (first picture) vs. a typical high power LED (second picture):



Those beamshots, when taken with a camera in manual mode, are great tools to compare the output power, tint, and radiation pattern, so these are the prefered way to compare lights so that others can appreciate their differences. Back on the CandlePowerForums we have many experts in the incandesent arena for the high power bulbs - also called "hotwires" - so I am not going to cover much more here since those are not my specialty.
Last edited:


Well-known member
Jan 10, 2005
Texas, USA, Earth
Re: Introduction to modyfing flashlights ...

Modifying flashlights - Part 2

by William Quiles

December 2009

LED lights:

To me, LED lights are far more interesting, and that is why I concentrate most all mods on them. My first exposure to LED's were with the Luxeon 1W, 3W, and 5W LED's, that produce about 100-200 Lumens. But today we have single 3W LED's that put out about 200 Lumens, multi-die 8-10 watt LED's that put 600-800 Lumens, and some new, very large die LED's that go into the 1000-1200 Lumen range in the 30 watt range!

A quick (not complete) list of LED's used often today, starting with the older ones:

Luxeon 1w, 3w, 5W (old)

Cree/Seul P4 through R4 (various packages and die sizes; XR-E, XP-G, etc.) - single die - 200-300 approx lumens at 1Amp, vf = 3.5v (varies)

Seul P7 LED - quad die - 700-800 lumens at 2.8Amps

Cree MC-E - quad die - 700-800 lumens at 2.8Amps (individual LED's can be wired individually in either series, parallel, or combinations)

Luminus SST-50 - single die - 800-1000 lumens at 5Amps

Luminus SST-90 - single die - 900-1300 lumens at 9Amps

For reference:

XR-E die is 1mm x1mm
SST-50 is 2.25mmx 2.25mm

SST-90 is 3mmx 3mm

Here is a "group photo" to share. Unfortunately at the time all I had was a broad point permanent marker, but it goes (left to right): XR-E Q-bin, MC-E, SST-50, P7:

LED's are current controlled devices. You don't light them up by using a regular/traditional voltage regulator - you need a regulated current source to drive LED's to their potential, so you need special "drivers" meant for LED's. The current through the LED as a function of the voltage is logarithmic - a small increase in voltage leads to a huge increase in current (more on these below). Good thing is that with the popularity of LED's, there is a good number of companies offering LED drivers, from the low cost Asian vendors:

To the very best quality drivers and my most used, the LED drivers from TaskLED:

The size of the batteries restricts the size of the host, and the bulb/LED being driven dictates what types and how many cells are needed. This is not a complete list, but here is a list of the common cells we use:
- CR123 - Non rechargeable - 3V cells. Used in almost all SureFire flashlights.
- Alkalines - Non rechargeable, low current applications only, due to their relatively high internal resistance. Nominal voltage 1.5V
- NiMH - rechargeables. Capable of high currents 5-10 amps, although cell voltage sags quite a bit at the high currents. Nominal voltage 1.1-1.2 volts
- LiIon - most popular cells, used in almost all laptops. High energy density, possible high currents, relatively dangerous cells unless a protection circuit is used to prevent short circuits, over-discharge and over-charge. Nominal voltage 3.7 volts.
- LiMN - much safer chemistry than LiIon, although not as high energy density. Can handle even higher currents than LiIon. Nominal voltage 3.7 volts.

First, a little nomenclature on batteries. The first two digits refer to the nominal diameter, the next two are the length in mm, and the last is the shape, 0 being a cylinder:
26500 = 26 mm dia, 50mm length
26650 = 26 mm dia, 65mm length
18650 = 18mm dia, 65mm length

Note for reference:
- the "C" Mag body takes C size cells, which are 26mm in dia
- most all of the Surefire lights take the CR123 cell, which is 16mm in dia

Battery capacity is usually stated in mAH, but the voltage of the cell is important when looking at the energy density. For example:
AA NiMH - 2900 mAH (1.2V)


18650 LiIon - 2200mAH (3.7V)

Available watts:
AA NiMH - 2.9 * 1.2 = 3.4 watts
18650 - 2.2 * 3.7 = 8.1 watts

This wattage is important since it gives an indication of runtime - how long will the particular combination of LED/battery/driver will last.

For example:
LED is rated at 3.7 volts and 1 amp
LED Driver efficiency is 90 %
Batteries: 2x 18650 cells (2200mAH @ 3.7V)

Power required to run LED = 3.7 * 1 = 3.7 watts
Power available at batteries = 2* (2.2 * 3.7) = 16.2 watts
Power available to LED = Power available at batteries - Power lost at driver = Power available at batteries * Driver's efficiency = 16.2 * 0.9 = 14.6 watts

Approximate runtime = Power available to LED / Power required to run LED = 3.9 hours

So a valid question would be, why use a driver if I am "only" getting 90% efficiency? Why not drive the LED straight from the battery, in what is called a "direct drive"? Bacause the LED is a current controlled device - it can't tolerate a high voltage applied directly since. In our case, the voltage of the two 18650 cells is 7.4 volts, which is WAY higher than the rated voltage for that LED of 3.7 volts - basically it would kill the LED instantly!. You can however drive the LED directly from a single 18650 cell, since the nominal voltage for the cell of 3.7 volts is the same as the rated voltage for the LED at 3.7 volts, but a couple of things need to be taken into account:
- the LED's actually have a "range" of voltages that can be as low as 3.1 volts to as high as 3.9-4.0 volts
- a charged 18650 cell actually rests at 4.2volts from the charger, and the higher the capacity, the less it will sag under load to the nominal 3.7 volts
=> if your LED is a low voltage (called vf - or forward voltage) and the cell is a high current, high capacity cell, you could be seriously over-driving or killing the LED. True, since there is no LED driver, the efficiency is by definition 100%, but also keep in mind that the brightness of the LED will decrease as the battery drains.

So basically LED drivers have a couple of advantages:
- you can have much longer runtimes by starting with a voltage much higher than the vf of the LED. The regulator will maintain the rated current to the LED as the batteries drain, to the brightness will remain the same through the whole run.
- by adjusting the current, the driver will provide the right current regardless of the vf of the LED - no risk of over-driving, damaging the LED (unless you set the regulator to a higher current value above the "rated" current for that particular LED).
- regulators offer the ability of having various brightness levels (like low, med, hi, and strobe/SOS).

Besides needing a proper current driver from your LED, you have a special requirement when using them - unlike bulbs that emit/radiate heat into space/air, LED's transmit heat through their mounting base, which means that just like CPU processors, you need a heatsink in order to remove heat from the LED - otherwise the LED will over heat, lower its output, and eventually die. And yes, LED's give you lower output the more they get heated, so temperature control is very important for LED's to give you their maximum rated output.

Now, the size/material of the heatsink in a handheld flashlight is NOT the real problem. The problem is how to remove heat from the body of the flashlight, once the heatsink has done its job (regardless of how efficient/fast) and moved the heat away from the LED. I have done a LOT of overclocking on PC's, and that is the best possible way to learn about heatsinking, and how to remove heat, or more appropriately to exchange heat/energy.

On a flashlight, there is no "forced" method, like a fan, since that would take energy away from the batteries and give us a shorter runtime. So basically we have only convection, through air, or through our blood:
1) The air surrounding the light. Some minor improvements can come from fins, to increase the efficiency of heat transfer to the surrounding air (again a lesson learned from CPU heatsinks), but of the two methods this is still the least efficient way since we don't have a fan blowing through those fins.
2) Convection to the hand holding the light - the blood in your body acts as a cooling system removing heat from the flashlight. This is the most efficient way, for a handheld light that is not under water (like a diving light).

Both methods will remove heat up to a point, and then the temperature will keep increasing since there is only so much the air/blood can remove. Anyone who has used a powerful LED/incandescent flashlight has experienced the flashlight getting warm and eventually hot, to the point that it is no longer comfortable to hold. So what does all of this manbo-jambo means:
- A single MC-E or P7 driven at spec in a handheld Mag body will eventually get too hot to handle, regardless of the heatsink used. It is simply physics: you have approx 3.5Volts at 2.8 Amps for approx. 10 watts of power that have to be dissipated.

- ALL LED's are rated for Lumens at a relatively very low temp, usually lab-controlled, at around 25C/77F (per the many data sheets that I have seen). That is basically room temperature. As soon as you turn ON your LED light, the output will start dropping since the temp on the heatsink will start going above room temperature.

- The temperature will keep increasing until some equilibrium point, depending on the air temperature, or how much pain you can stand while holding the hot light, etc.. - note that in the case of LED's this equilibrium point will almost always be higher than the rated temp at which the LED was giving its "rated" output. Those 700-900 lumens are not possible long term on any handheld light that is convection cooled (air/blood), since the temp of the LED will quickly go over the 25C.

- A light with any multiples of MC-E or P7, HAS TO GET EVEN HOTTER, and will get hotter much quicker than the light that has only one MC-E or P7. You are basically adding roughly 10 watts per each of these high-power LED's. The degrading on LED output happens even quicker when using multiple MC-E/P7 since the "shared" heatsink gets multiple times the heat, so the output gets lower and lower with time.

- The larger the heatsink size/size of the body, the more heat can be absorbed by the body, up to a point. This is why you can hold much longer in your hand a Mag-size P7 light than a single CR123-size light driving the same P7. If the host/heatsink size is the same, you will reach this "darn! - this thing is too hot!" point sooner with more LED's.

Heatsinks for LED's can be bought, specially for the ubiquitous Maglite platform:

or they can be totally custom to fit the job at hand:


It is important to note that most of the time the heatsink is hollow to allow the LED driver to be housed in there - this saves precious space, and also gives the LED driver a thermal path, as some components on the driver also need proper/adequate heatsinking.


As with bulbs, but even more important with LED's, the choice of reflector has a huge impact on the type and quality of the beam. Here is a comparison of a wider beam, with less throw - less "distance", compared to a narrower beam with better distance:


Here perhaps is an even more dramatic example. The first photo is of an incandescent light with about 600 lumens. The second one is a high power LED with over 2000 lumens, but in a much wider pattern:


Although LED's tend to be more "bluish" and not show the right colors at night when compared to a well driven bulb (see above), LED's are now becoming available in so called "warm tints", which sacrifice a little output for a nicer and more natural tint. Guess in this picture which LED has the warm tint and which one is the standard cool white tint:

=> The neutral tint is on the left ;)

The difference is not night and day, but I do prefer how the natural tint LED's make grass/trees/foliage look more "natural" to me. First the P7 cool white, then the MC-E neutral tint:

Last edited:


Well-known member
May 17, 2008
London UK
Re: Introduction to modyfing flashlights ...

A very informative post Will :thumbsup:




Well-known member
Mar 22, 2007
Re: Introduction to modyfing flashlights ...

Thanks......but can you go into more detail????:crackup::crackup::crackup:


Well-known member
Jan 10, 2005
Texas, USA, Earth
Re: Introduction to modyfing flashlights ...

The "device" is called a "peg vise", and credit for this little tool goes to forum member "darkzero". To find one, just search on Ebay for "peg vise" ;)

Black Rose

Well-known member
Mar 8, 2008
Ottawa, ON, Canada
Re: Introduction to modyfing flashlights ...

Thanks Will.

Lee Valley tools carries them for a little bit more than what they are on eBay, so I can go over to the local store and grab one.

One of those would have saved me a lot of hassle when building my P60 drop-ins.


Well-known member
Nov 6, 2007
SF Bay Area
Re: Introduction to modyfing flashlights ...


You sure have done some awsome work; thanks so much for sharing this wealth of information. :thumbsup: