Monster 7,500 Lumens 100W LED Flashlight for under $10

I discovered that due to a lucky co-incidence of voltage and internal resistance, a 100W LED can be connected directly across the terminals of two 18V Nickel Cadmium power tool batteries. And that means you can build a 100 Watt (7,500 Lumens) flashlight for less than $10 (not including batteries).

Note: Don't try this with other battery types - you'll almost certainly fry the LED!

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Author glen buchanan (8 days)
20meg ohom resister should be used little current but pressure from voltage

Author PhantomAct (3 months)
Seems useless to build an LED that you can light up for a couple of
seconds... can you make it light up for longer?

Author dell177 (14 minutes)
You need a good aluminum finned heatsink if you want to use this for more
that 10-20 seconds or the LED will destroy itself. LED's get very unhappy
if they are over driven or if not heat sunk properly. Did you measure the
voltage across the LED while it was lit?

Author Anton Nym (1 day)
Nice bit of work. I had no idea LEDs got very hot. Have you considered
water cooling with a small radiator and fan? It would take power from the
battery, but it looks to me like you have power to spare. If you could get
enough cooling, say for a walk around the block, that would be most
excellent. Keep up the good work!

Author Marty Vargo (4 months)
Polish the metal to a mirror finish and then use thermal paste in between
the metal and led and you will have great heat transfer.

Author Junaid Khan (16 hours)
Neat work Julian. Do you think there is a possibility to engineer the led
heat sink which can either use the heat to heat air and use it as a warm
air heater to warm a room or even warm water and store it in a tank for
later use. As well as heating air or water could you use the same hear to
generate electricity and store it in a battery. Would it possibly do all
three. Heat sink heats water which turns a small fan which gets heated as
well so the fan when it turns will blow warm air under the heat sink which
is also warm and the water which warms goes in front of the fan below the
heat sink via thin pipes. So the fan gets warm via the heat sink so when
it does spin it blows warm air in and around the heat sink. fan turns by
electricity made by led heat sink as it warms water creating jets of steam
and the rest of the warm water goes around some quick heating pipes and
into a storage tank. Sounds like a long shot but not impossible. Only
thing is how would you keep the led from blowing out. Could cool the led
from where the light is by some cold metal sitting on the light or just
above it. Thanks.

Author darryl barton (6 months)
I especially appreciate your battery holder. That's clever.

Author Faleh alarabi (1 month)
Julian llett , I live in a farm with no electricity and I use an engine to
produce electricity when I need it , will I be able somehow to charge any
kind of batteries that I can use when the engine is running out of fuel ?
and can I charge them by the engine itself ? thanks mate

Author patrick donegan (13 hours)
what about 1 battery?

Author intriq8 (2 days)
Yeah, the title is highly disingenuous. Add a constant current
step-up("600W") for $7-8, and include the price of a power source, AND
heatsink. If you're talking scavenging, then it's the "build a SEM for $1"
type of slippery slope. The sad/nice thing is that you've made about $5000
dollars on this one so far, right? off this deceptive and mostly
useless/misleading video? So you're incentivised to make more disingenuous
titles. I guess that's how youtube works: a lot of misleading the ignorant.
I like your content on the whole...but this kinda makes me want to
unsubscribe on moral grounds. hah. absurd.
Funny; somehow I can't see you amending the title on this little earner...

(and what would it be?? "I use parts I already have (with an off-the-shelf
value closer to $100) to briefly light a 100W LED, in a way that is not
feasible or useful to me or anyone" ? actually that title might intrigue
somewhat, just not as much as the blatant misrepresentation does ;)
while i'm pitching titles, i've got a nicer one: "Briefly light a 100W LED,
with parts you may already have, in a way that is neither technically nor
economically desirable for long term, but may interest you for the sake of
Either of those would be fair ;)

Author Bill James (27 days)
Brilliant demonstration and build. You might try looking for an old DELL
PC in that skip. DELL made huge heat syncs for some of their comps that
used a plastic duct to a fan in back of the computer case. Hmmmmm? use
the duct and big fan to mount to a small amuminium box to mount your
monster LED to and you may be able to get a full minute before to have a
mini supernova. This would be great Light to signal airliners to land with
after the BIG EMP destroys most of the unshielded electronics in the

Author davidswelt (25 days)
So what you've effectively demonstrated is that you cannot custom-build a
100W LED flashlight for under $10. Your chosen power source cannot be
bought for that price. It is also way too heavy and bulky for a
flashlight, as the batteries and the heat sink you need make the
contraption obviously impractical for a portable flashlight... Question..
Does the current stay constant as the batteries deplete and voltage drops?
(Are constant-current drivers all that expensive?)

Author Inu Yasha (15 days)
Hello +Julian llett, I have a pretty common question for you: How many mah
of battery should I have in order to make this LED last at least 8 hours?

Author Jonathan Snipes (7 days)
Hmmmm like the light but couldnt you use a heatseat fron a computer that
has a fan attached to it and then use some thermal paste and wire it in
with a diode to run at 12 volts, and you can even get a fan that will run
same voltage as the batterys are you can run it off one as the light runs
off both batteries, i have done this and i get a good 4hour runtime and i
even made a case around it so it will look like one of those old train
lanterns, it even has a switch to turn both light and cooling fan off are
on. Good vid though.

Author Povil Ka (1 month)
With your useless, miscalculated and - in general - stupid - "invention",
you wasted few hours of Your time AND time of 1183120 people (at the time
of writing).

Lets do the math:
You video took 6 minutes 30 seconds.
That equals to 128171.33 man-hours, or 42723.77 work-days or - in other
words - you wasted 14.63 YEARS of productive effort of the man-kind.

Think before you post.

Author Terence Kearns (12 days)
"So, I'm just gonna do it again, with not NOT pointing directly at the

LOL! that cracked me up so much...

Author tigmonx (2 days)
Incredible... This give me so many ideas.

Author VIC LIC (17 days)

SET -- 100W Watt LED Chip weiß + Trafo Treiber Driver KSQ + Alu Kühlkörper
EUR 88,88

Author MaxxHuey1 (3 months)
I am just guessing, you will need a 100 watt LED driver to regulate the
amount of current otherwise you will eventually burn out the LED anyway
even thought you have the correct limiting voltage. The is because as the
LED gets warmer, the resistance across the LED start to get lower allowing
more current to pass through, this vicious cycle goes on until the LED burn
out... Please correct me if I am wrong... :-)

Author cheapo911 (13 days)
7500 lumens my ass. 

Author David AE Levy (1 month)
lol this made my day, thank you!

Author Thor Rankin (1 month)
No no no. Just no. The steel 'heat sink' is ridiculously undersized. You
say balanced sweet spot that will not damage the led. That is nowhere near
the 40VDC you are throwing at it. With that 'heat sink' you are probably
looking at more like 10VDC if you are lucky for extended usage. To properly
cool a 100W led you would need a huge passive heat sink or a fairly large
actively cooled one. It's a fun experiment, but by no means a flashlight,
or a good guide on how to build one.

Author TheBigWWI (5 days)
Just curious, do all Brits have that weird little retard thumb?

Author Andreas Kötter (1 month)
Sure, the batteries are for free right? What? They cost 60$ each? Hmmm...
then this isn't 10 Bucks ...!!!

Author Lawrence Mudge (10 days)
You need to add heat sink compound in-between the back of the LED and your
heat-sink. Not many people have two 18v rechargeable batteries available

Author jimvandamme (3 months)
You won't get 20,000 hours out of your flashlight unless you carefully
control the heat and current of your LED. Then again, you are not going to
run it for that long anyhow. It's the internal resistance of the batteries
in series with the resistance of the LED that limits the current. Heftier
batteries would have less resistance and be worse for LED lifetime.

Author Donavan Aarons (16 days)
Buy a LED driver... Will run cooler and safely

Author Jefferson Asejo (4 months)
its hard to carry your flashlight because it is very big

Author Abdullah Bilik (19 days)
10 Dollars? how much id the battery packs cost?

Author OfficialHardtechnoChannel (5 months)
Sorry Julian, but this is sensless since there is no current limitation in
the circuit. Even in short turn-on intervalls, the led can (and will) take
damage due to the hughe amount of current.

Author Arcadio Munoz (1 month)
Would this still work with 18V Li-Ion batteries from a cordless drill?

Author Chemtrailfan (24 days)
I think is enough to tell the costs in pounds because Americans won't like
this product too much :)

Author אלי ארבל (8 days)
it must have cooling.

Author thefotoman2010 (1 month)
Dass diese dämlichen knödel-englisch-Typen immer ihre halbe
Lebensgeschichte erzählen müssen. Kein Deutscher würde so viel erzählen.

Author Harry Roberts (22 days)
The heat is wasted energy, can you use different batteries to power the
LED without it overheating?

Author nino -aka (28 days)
waste of time

Author Jonathan Snipes (7 days)
I meant to say you could use not couldnt my bad.

Author nicholas cremato (2 months)
Next is to use an old magnifying glass as a lens and away we go! 

Author Loren Husky (2 months)
Could these be used to grow plants?

Author Nick C (1 month)
Maybe see if there's a CPU heat sink that is of equal size and can be
mounted to the back with thermal paste and a fan?! I'd guess this could
work for a few minutes or longer. There must be a way to cool it properly
or they wouldn't have produced it, so what is the application that you find
this in?

Author OlivierAstuces (4 months)
If I'm not wrong, when you touch the copper at the end, you are touching a
wire that supports a 36V 3A current. Does it hurt ?

Author Jason Leo (2 months)
sorry but this video is complete shit. firstly how is it a lucky
co-incidence you can use 2 18v batterys? loads of batteries exist and
therefore it would be always possible to find 2 to work and secondly whats
with the fake title to get views? ryobi batteries are what £30 each so to
make this would cost £70 for yours or £30 using cheaper batteries. so no
you cant make this for $10 dollars because without batteries its half made

Author Youtube Admin (1 month)
that LED would be nice inside of a car xD

Author chillzwinter (1 month)
You could just solder 27 NiCd batteries together for $50. At 1000mah you'd
get 20 minutes continuous use - and closer to the exact voltage spec.

Author Garage and Garden (28 days)
Have you done any issues with heat dissipation?

Author Joseph Perrotta (2 months)
The sellers spec sheet says 32V to 34V. The combined full charged voltage
of a 18V battery is around 19-20Volts. That being the case you would be
pumping at least 36 to 40Volts into this LED How long do you think it will
last before you burn it out?
It may work well for a few seconds give it 10 minutes with a 36V ebike
charger attached to maintain the voltage. See what your results are then!

Author mj rooney (1 month)
You got to much time on your hands, if you need an led torch cheap go in
one of those shifty pound shops and buy one you stingy old bastard

Author girlsdrinkfeck (1 month)
id use the biggest CPU heatsink i can buy

Author Craig Nehring (2 months)
Is there a lower voltage sweet spot that will illuminate that 100 watt LED
but will not generate as much heat and at a reduced lumen output?

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