Introduction: 21 W Led Bulb (1450 Lumens)

Picture of 21 W Led Bulb (1450 Lumens)

I wanted a high output LED bulb for use in an exterior motion detector lamp.  The high efficiency bulbs are no good as they take time to warm up, and the LED bulbs available are too low output.  Normal bulbs consume a lot, and need to be replaced often.  So I decided to make one.  The leds should last 100,000 hrs.  I am guessing that the transformer will go out first.

Material needed:
-230 VAC - 12 VDC transformer
-LED ribbon (I used 1.8m of SMD 5050: 12W and 800 lumens /meter)
-Empty beverage can
-Electrical tape
-FBS glue

1) Make sure can is not too big to fit into enclosure (also remember that the led strip will add about 5 mm to the diameter)
2) Cut off top of can, and put some electrical tape on cut edge, as it is sharp and can cut)
3) Drill a hol at the bottom of the can (want to let the condensation moisture be able to escape.
3) Solder output of transformer to led ribbon cable lead
4) Starting at bottom, remove back side cover (to expose sticky part) and coil the led strip around the can.  You might first want to try doing it with the protective shield still on. 
5) Add some silicone glue (I use FBS) to both ends of the strip.  Apply generously, use some tape to secure the piece in place while it cures overnight.
6) Remove tape and Voila!


BigAl67 (author)2013-03-31

Great Stuff!! I'd love to build this! Where did you source the LED's from?

hofweek (author)BigAl672014-03-20

great try

skwoorl (author)BigAl672013-03-31

Big Al, try

triumphman (author)2013-07-15

You guys are making it too complicated! KISS!

Blackice504 (author)2013-05-06

Nice work, i posted a reply to waltbosz that asked the question of heat, but anyway, i also thought about the P.S.U for these i see you used a Transformer which is great as many people have many of these spare around the home, but if you going for Efficiency a switch mode PSU comes to mind there are chips out and about some give Free samples, also those CREE L.E.D are very bright and might be the same cost as your L.E.D Array.

Great work lets hope that people will use it, as L.E.D are the future for lighting, also there safer then the Energy Saver Fluro lights as they can produce some side effects that are not good for babies, i do not know how accurate that is but i have herd about that and some people getting headaches from the.....

Also if you going to use those Transformers outdoors can rust or your contacts a good way is to resin all the electrics with some circuit board lacquer or Liquid Electric tape yes i said LIQUID.. most Electronic shops should have it, Try it i am sure you would love it.

waltbosz (author)2013-03-27

Neat idea, but what about heat dissipation ? Commercial LED bulbs have heat sinks to draw heat away from the LEDs. I'm not so sure your aluminum can provides enough surface area to act as a good heat sink. Let us know how it works out.

Blackice504 (author)waltbosz2013-05-06

you will find that these type of L.E.D's do not produce much heat secondly you will also find most of the heat comes from the P.S.U in the case of GU5.3 (12v down lights) they have a DC-DC converter , in the case for GU10 there 240 volt they have a step down in them that produces allot of heat thus needing a heat sink, in fact i feel that some of these lights are loosing Watts via Dissipation on there P.S.U i would love to know how many watts are lost in the P.S.U and how many watts go into the light it self.

In Short when buying these L.E.D lights read carefully for example i seen a 10WATT L.E.D down light that was 240 Lumen vs 9.5WATT 350 Lumen i would assume the L.E.D where better design and maybe the P.S.U was better as its heat sink was smaller.
I hope this helps.
one more thing these are the SMD L.E.D the commercial ones are normally CREE or something like that "heat sinked" however i have seen these used in light bulbs for cheap $9.00 here is a link. please note could not find the cheap $9.00 one but it looks the same.

peterbd (author)waltbosz2013-03-28

It this case I am not worried about heat dissipation. This is used in an outside motion activated setting. On for 20 sec at a time. However, I am going to do some more testing on the heat. I am waiting for some warm led strips and than will make a new version.

starphire (author)peterbd2013-03-31

I had the same concern. Dissipating 20 Watts worth of LEDs in such a small area isn't a problem for such a limited duty cycle. But you would probably save somebody a very disappointing experience by emphasizing that limitation in the introduction to your instructable, since many people won't think of that. It may never even be a problem at full duty cycle as long as they have good airflow around it. But woe to the person who thinks they can put that inside a fully enclosed fixture and leave it on for hours at a time! That's one reason you don't see 100W-equivalent LED bulbs yet - not enough heat sink area for the current state of LED efficiency (this will change within a few years, though - they are getting better all the time).

chandshar (author)starphire2013-04-18

By using a small 12v heatsink fan inside the can with both ends cut off and a pepper pot set of holes set appropiatly in the outer enclosure would help with cooling.
But as the original was only for motion detection and on for short times and not enclosed and used outside there would be no problem and is a good base idea to further ideas as several have been sujested already

barrem01 (author)starphire2013-04-01

Your point about the importance of heat dissipation is well taken, however there are 1750 lumen (100 watt equivalent) led bulbs available now.

TikiTime (author)barrem012013-04-02

the LEDS on that page are averaging 100 lumens per watt, so the 13 watt led bulb produces 1300 lumens.. if the efficiency stayed the same we would see a 100,000 lumen 100 watt LED bulb...
Great for out door lighting, but too bright for indoors unless you are lighting from 20 foot high vaulted ceilings, and even then you'd want to be able to "turn it down"

jimvandamme (author)TikiTime2013-04-03

I'm sure he meant "100 watt incandescent equivalent". Because folks are still not used to thinking about lumens.

starphire (author)TikiTime2013-04-02

That isn't going to happen in the form of a screw-in replacement light bulb. 100k lumen LED fixtures do exist, and will become more common in outdoor and high bay applications. Unlike an incandescent filament however, LEDs simply cannot survive temperatures of hundreds of degrees, so to safely dissipate 100 or even 50 Watts away from a group of LEDs you must either have a rather large surface area, active cooling such as fans, and/or technology such as heat pipes. It just makes more sense in high-power applications to replace the whole fixture with something designed specifically for LEDs. Someday the Edison base light bulb and its replacements will only be seen in museums and antique light fixtures. Good riddance.
In the meantime, 15-20 Watts is probably the most power we'll see LED replacement light bulbs using with proven technology, but there are already 150 lumen/Watt LEDs coming out of the labs and 200 lumens/Watt appears achievable. So more light for less power and cost is a pretty sure thing.

barrem01 (author)TikiTime2013-04-02

"100 Watt equivalent" means "roughly the same luminosity as a 100 watt incandescent bulb" The point of the technology is to get the same amount of light at a lower power consumption, not to build an led bulb that actually use 100 watts of power.

starphire (author)barrem012013-04-01

Interesting. I wonder why I haven't seen any of these at my local hardware store? I suspect it will still be a while before any of these comes down in price to something approaching the ~$13 floor I'm seeing now for 60W-equivalent LED bulbs.

aking14 (author)2013-04-06

If it were 100% efficient, there wouldn't be any heat at all regardless of the energy being converted and sent out as light.
If it's 20W total and 60% efficient, that only leaves 8W wasted as heat. 80% leaves 4W, etc. The strips get warm, but I wouldn't be concerned about starting a fire wrapping a few around a can. The strips are fine at continuous duty. Might get warm if you stuck 5m into a large wine bottle or similar, but even then I doubt you'd be talking incandescent bulb temps, and they put out a good amount of light.
Also remember that bulb lumens are typically going out in a near sphere, while LEDs are typically optimistically rated for the same but in only their much narrower beam angle. Even a wide 120 deg angle LED will probably take 6 or 8 to fill an entire sphere, and put out the light you'd think from the 'lumen' rating, to compare to a bulb. Did the numbers years ago, and it's like 1100+ 20,000 mcd 20deg LEDs to equal a 100W bulb in light output. Takes a lot just to fill a sphere, and then many spheres to equal the light level. Requires a lot of backtracking the measurements and thinking and math to make sure you are comparing apples to apples with LED vs incandescent bulbs, if you do it without writing it out and double checking everything the answer you end up with is usually wrong, or only right by accident.

cstogner (author)2013-04-04

Could you recommend a good LED ribbon source and a warm LED source per your comment below?
The material list implied that the LED ribbon was cut, but not stated as to how to best handle that?

peterbd (author)cstogner2013-04-05

You should be able to find them on ebay for about $12 for 5m. Search for "led" and "strip". Additionally add "warm" or "cool" depending on the type of light you want.

jimvandamme (author)cstogner2013-04-05

On eBay, you'll find lots of peddlers of LEDs on 5 meter reels. The ribbons have terminals and "cut here" markings every 5 cm or so, thereby you can adjust the light or size to suit. However, seldom do you find data on lumens, color rendering, or efficiency because the sellers are clueless. A good place to learn about LED strips is where they explain the different sizes & light output. I'm not saying their prices are the best.

Antzy Carmasaic (author)2013-03-25

Nice idea!
It will be even better if you could use a CFL bulb base as enclosure. That way, it can plug into a household bulb socket as well...


Now I know why I save blown CFLs. The base, and all the electronic goodies inside (that still work).

cstogner (author)jimvandamme2013-04-04

Is there an instuctable about how to best disassemble the CFL to avoid mercury contamination?

jimvandamme (author)cstogner2013-04-05

Here's my micro-instructable: basically you just need to avoid cracking the bulb. I take a hacksaw to the joint between the 2 white plastic shell pieces. They just snap together, but are hard to get apart. You can cut it all around to get a clean cut, or just make a slot to get a screwdriver in to twist it apart. Once you get two pieces you can snip the 4 wires to the bulb and recycle that.

Wallwart in the CFL base

Exactly what I was saying.

peterbd (author)Antzy Carmasaic2013-03-28

I That is a good idea, but in this case I didnt have the room for the extra depth.

Antzy Carmasaic (author)peterbd2013-03-28

look at the video in this page:

I'm sure you'll like it. Just what I was mentioning in the above post.

rmd6502 (author)2013-03-29

That's a great idea - by transformer do you mean wall wart? Otherwise does the reverse voltage harm the LEDs?

wa7jos (author)rmd65022013-03-31

LEDs work fine on AC. They turn on for the half cycle when they are forward biased, and off on the other half cycle.
A DC wall wart is fine, but you need one big enough for the job. Note that the flex strip consumes 12 watts per meter. W = V * A, so at 12 V, that's an amp per meter. You will need one rated at 2A or better for this project.

luvasu (author)wa7jos2013-03-31

Protect with one rectifier diode in series.

agritzmacher (author)luvasu2013-04-02

LEDs ARE diodes. No need.

lsymms (author)luvasu2013-04-01

A better option which greatly reduces flicker would be to wire 2 strings in opposite directions so strand 1 shines on the high voltage part of the cycle and strand 2 shines on the low voltage part of the cycle. You will still get a hint of a flicker but your LEDs will be very protected. You can use film caps to reduce the length of the strands. I'll try to find the circuit design I used to size the caps and reply back.

steveastrouk (author)wa7jos2013-03-31

No. Read the specs. They have a maximum reverse bias voltage: exceed that and they go "poof".

wa7jos (author)steveastrouk2013-03-31

That is true, but I was looking at it from the perspective of the complete circuit.
These strips have three LEDs and a current limiting resistor in series.
The forward voltage on white LEDs is usually in the neighborhood of 3V.
That makes 9V for the three LEDs, so the resistor has to burn up the rest, 3V/20ma=150 ohms.
The resistor is what prevents the LEDs to go "poof" when reverse biased. That, and the spec that the reverse voltage is about 5V.
So, if we put 12VAC (rms) into the circuit, the peak reverse voltage is about 17V, and the LEDs (with the resistor) can handle that.

rmd6502 (author)wa7jos2013-03-31

But a reverse-biased LED doesn't conduct nearly the current of a forward-biased one (nanoamps or even picoamps), so the voltage drop across the resistor is much lower than the 3v when forward-biased. Poof?

steveastrouk (author)rmd65022013-04-01

That's right. The CORRECT way to wire them on AC, is either with a blocking diode, or wire them in anti-parallel, so half of them light on one half cycle, limiting the reverse voltage on the other half to one forward volt drop, and then changing places on the next half cycle.


peterbd (author)rmd65022013-03-30

I dont know if reverse voltage harms the LEDS. They will simply not shine if the polarity is reversed. The LED strips can usually be cut if sections of 3 leds. You will see labelling on the strip for + and -. If using an rgb strip, then you will have 4 connections.

starphire (author)peterbd2013-03-31

As long as the peak reverse voltage doesn't exceed the maximum reverse voltage of the LEDs x 3, it won't harm the LEDs. However, especially without any kind of rectifier or capacitor to smooth things out there is a risk that a brief (i.e. microseconds-long) voltage spike or surge on the AC mains side will exceed that limit, and that can be long enough to damage the LEDs. Such urges are common during electrical storms in the area, or when heavy duty motors start up nearby, etc. - in other words, unpredictable events leading to mysterious failures. Protection can be achieved in various ways, such as a high-current zener diode rated for just above the normal peak voltage, or a transzorb device. Or just use a transformer with a DC output on the inside; they are so cheap and common, esp. with the switching-type ones these days (small and light compared to old fashioned transformers, and more efficient too).

Treknology (author)starphire2013-04-01

If the reverse bias voltage is such a concern, use a bridge rectifier..

steveastrouk (author)Treknology2013-04-01

OP SAID he used a "DC transformer"

Treknology (author)steveastrouk2013-04-01

I should have attached my comment to thread above.

pjhrtr (author)2013-04-01

Have you considered adding a 5v PC ventilation fan in order to maintain the light duration?

mgcchkn (author)2013-03-31

Any pics or video of this thing in action?

Mark Rehorst (author)2013-03-31

It's great for the intermittent duty you have planned for it, but there is no way that it will work for being fully on for more than a few seconds at a time. Estimating 100 lm/watt (generous), you are burning about 15 Watts. If you want those LEDs to last, maybe instead of a timer you should put a temperature sensor on the can and shut the light down when it reaches some specific temperature, maybe 50 or 60 C. High operating temperature will reduce LED life to far below the manufacturer's spec which is based on ideal conditions (i.e. low temperature).

bennyj121 (author)2013-03-31

The first thing that popped into my mind when I saw this post is how you cut the top off of the can. If you sand the top rim of the can (grind, file, scrape on concrete, etc) you can separate the "can" from the "top" and leave a lip around the top that is not sharp and also provides structural integrity. Give it a shot, it's way easy and can make this a bit safer.

larsrc (author)2013-03-31

Nice idea. If heating turns out to be too much of a problem, I suppose one could mount a little fan at the bottom of the can and cut off the top.

storre (author)2013-03-31

I wouldn't worry too much about heat. I have 10 meters of this 5050 light (without waterproofing) on a 75mm PVC tube about a foot long. I use 4 of these lamps so 40 meters total on a 20A power supply. Works great in the hot summer and no problems with heat. I slip that inside one of those Chinese ball lamps. Puts out a LOT of light. I put a little 6" blue strip on the inside bottom of the PVC just to give some effect :)

rimar2000 (author)2013-03-31

Clever idea!

doc_cls (author)2013-03-26

Could use large-diameter PVC pipe as the mounting surface for the LED strip as well.

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