Step 4: Selecting the LED's

I am using the Philips Luxeon LED's. Currently they are the most widely available power LED's at the lowest price (about $3 for both 1-watt and 3-watt stars). the place to buy these is direct from the distributor: http://www.lumiledsfuture.com (same as http://www.futurecb.com) - everyone else sells them at a huge markup. Undoubtedly other brands will become more available in the future.

The Luxeon LED's are available in a couple of formats - the most useful is the "star" format which has the LED already attached to a small heatsink. this is far easier to work with than the bare LED.

The Luxeon LED's come in both "1 watt" and "3 watt" stars. the difference between these is actually a lot less than the names indicate and they are priced nearly the same also (about $3 each). in reality, my tests show that with a large heatsink the "1 watt" model is capable of 3 watts output, while the "3 watt" model is capable of 4 watts. the "1 watt" model is notably very conservatively rated, it is really more like a 2-watt LED. the caveat is: the LED's efficiency drops with increased power (2 watts gets you about 65% of the light output of 4 watts), and lifetime may also be reduced (they are rated at 50,000 hours though). so if you are making a light for occasional use and want maximum output for the $$$, feel free to run the LED's considerably over spec. if you want an efficient room light for long-term use, stick to 2 watts on the 1 watt model, and 3 watts on the 3 watt model.

the other important difference between the 1 watt and 3 watt stars is that the 1's have an insulated heatsink, while the 3's do not - that makes the 1's a little easier to work with since you can mount them directly to a heatsink. the 3's require using an electrically insulating film between the star and the heatsink. (see the step on heatsinks).

other options:
- do you want a spotlight or a room light? if you want a room light, get the "batwing" or "lambertian" LED's. these shine light over a wide angle (either 110 degrees or 180 degrees).
- if you want a spotlight, you can get the "Star/O" model which has a built-in lens. or you can get the regular batwing model and buy a separate lens for it which easily glues on. There are several companies making very inexpensive ($1) lenses for the Luxeon that let you make a 5, 15, or 25 degree angle spotlight. I've used these ones: L2Optics/Dialight part numbers OP-005, OP-015, OP-025, and lens holder OH-ES1 or OH-S35. Try this: direct search at Future.
- equalizing brightness/hue: the different color led's are not all equally bright at full power. the simplest light (shown in this project) uses one string of LED's in each color, so when you turn all three colors on full power, the overall hue is yellowish (*very* warm). that's because the blue led's are not as bright as the other two. so if you are building a larger light, consider using an un-equal number of strings of the different colors. if you use the Luxeon-1's, try 2 strings of blue for each string of green and red. with luxeon-3's, equalized-brightness requires using 4 strings of blue, 2 strings of green, 1 string of red. this is only important if you are mostly using this as a white/off-white lamp. if you are using it for an FX lamp, there is not much point to equalizing the brightnesses.

what I used:
I used 1-watt star LED's for my light (running them at about 2.5 watts each) because I had a bunch of them already, i'd recommend using the 3-watt stars if you are buying new ones since they cost nearly the same. i used 5 red, 5 green, 5 blue led's. part numbers:

more information: the manufacturer datasheets:
Phillips Luxeon Star LED's: http://www.luxeon.com/pdfs/DS23.PDF , http://www.luxeon.com/pdfs/DS46.PDF
L2Optics/Dialight Lenses: http://www.l2optics.com/luxeon.aspx

I'd recommend attaching one LED and running it at full power for a while to make sure that your attachment/heatsinking method is good before you do the rest of the LEDs. Three watts is nothing to take lightly -- they'll easily burn your fingers if they aren't heat sunk. (yep, I did that!) There are thermally conductive epoxies (basically epoxy with little bits of metal in it), so that may be an option. Check the electrical conductivity of this epoxy before using it with the 3W LEDs.
the point of this instructable is: i already did the trial-and-error work for you! i have tested the "GE Silicone 2" adhesive, and it works great with the 3-watt stars running at well over the rated power. as i mentioned above, feel free to do it the "pro" way if you want, but the purpose of the instructable is to show you some easier/cheaper ways using common materials that work just as well for this particular application.
<p>Hi I an new to this forum .I have been doing some research on Thermal conductivity of different adhesives and when mounting 3w. led's this is important. I have found when you are looking at a particular adhesive you want the highest &quot;w/mk&quot; # you can find. The higher the number the better it transfers heat from one surface to another. ie. silver has a number of 4.3 w m/k, aluminum has a number of 2.36 w/mk ,Styrofoam .03 w/mk. Arctic carry's a line of high # heat transfer compounds. ie. Arctic MX-4 Thermal compound that transfer number is 8.5 w/mk it all has to do with what is mixed into the compound to transfer the heat. Not all the compounds are adhesives though. Some you may need an alternative way to affix them to your heat sink. The most important thing is heat transfer than second should be attachment. </p>
<p>Hi all, I hate to admit it, but it's been twenty years since college algebra and I cannot, for the life of me, remember how to solve for two variables. Can someone- anyone- please walk through solving for R1 &amp; R2? It's killing me and I can't google the answer and i am running out of paper...... additionally, I am not talented at building electronics. I am attempting to build an exposure box for alternative photography techniques using H/O UV LEDs. I'm using 2.8v for my shut off voltage and 3.8 for max power. 2K or 2.5K for the potentiometer. 5 LED string x2 parallel, 28v total, 700ma LED string Current. I think that's information overkill. Help please! I want to learn how to do, so please show your work! Thanks! Johnny</p>
<p>Hi Johnny50,</p><p>if potentiometer 2K then R1=500 ohm R2=5100 ohm</p><p>if 2.5K then R1= 625 R2=6375</p><p>But your system will go hot, because the output is too much (28V). The ideal output would be 20V and 1.6 A.</p>
<p>Hello,</p><p>Which GE Silicone-2 did you use? From what I read there is a very wide range of them. (Or would any do?)</p>
I have really had a gut full of the electrical LED&nbsp; power supplies... wasting power and all the BS with the designs etc.<br> <br> So I came up with a VERY simple way to run and control LED's.<br> <br> Assuming the power supply is 12V - or on a charging car battery - say 14.2V.... or even 15V for the silver / calcium car batteries...<br> <br> OK just for simplicity's sake we will have a 12V power supply.<br> <br> Each LED has a PEAK forward voltage.... which is only relevant for the amount of current in the supply. I have run single 3.5V 20ma LED's on 240V mains supply with only teeny capacitors to limit the current&nbsp; - they were getting 200V... and almost zilch milliamps... and they ran quite dim.<br> <br> So OK assuming that the 3W LED's peak forward voltage is 3.9V.<br> <br> Each LED has an internal resistance - and with enough of them in series - they LOWER the available voltage to each LED - thus acting as the current limiter at the same time.<br> <br> So if we add 4 LED's in a string and run them on the 12V, we get a total peak voltage capacity of the LED's at 15.6V, thus giving each LED 3V - which is about 20% less voltage than the &quot;accurately regulated voltage and current supply&quot;.<br> <br> Less voltage = less current - so the LED's will also be a bit dimmer, but you will also have more of them...<br> <br> QED.<br> <br> It's really just a case of suck it and see.<br> <br> For 2.2V LED's on a 12V supply, I'd be using say 8 of them in series to start off with and then perhaps dropping to 7 LED's in the string.<br> <br> There is a magic point of about 15% less voltage than the peak forward voltage that gives enough resistance to stop thermal run away from occurring - and the light is still quite bright, and you have an extra LED or two in the series...<br> <br> AND you don't have to mess around at all with any BS current limiting circuitry.<br> <br> Doing the calculations, getting the parts, making the circuits, and they also tend to waste power etc.....<br> <br> This way - dead reliable, and slightly dimmed LED's last almost forever.<br> <br>
Hi Wrogerwroger, <br>you made a point here. In your 240VAC power supply example did you put the LED's as the rectifier diodes in a Greatz rectifier brigde driving the complete LED string to get no loss from the rectifier as well? The bridge LED's would be dimmer I guess than the rest.
Hey there, <br> <br>I tried to assemble a circuit like that with 4 SEOUL LEDs of each color (R42182, G42182, B42182), however the 10k slider I added does not seem to work like expected. <br> <br>With my 19V power source I can switch only between like 13.2V and 12.9V incoming to the LEDs. It joes does not dimm anything... <br> <br>No matter what resistors I use with R1/R2 (tried several combinations, even plain trial&amp;error), even without any resistors the circuit is just lighting. Without of course at maximum brightness. <br> <br>Anyone got an idea where I have failed here? (Also have some 12V computer power supplies laying around if that would be all it takes...)
Wow, your way is a lot more complex than mine. I basically take a full voltage and a nail and bolt and just place it on the heat sink.<br /> <br /> <a href="http://www.learningaboutelectronics.com/Articles/Why-attach-a-heat-sink-to-a-voltage-regulator" rel="nofollow">http://www.learningaboutelectronics.com/Articles/Why-attach-a-heat-sink-to-a-voltage-regulator</a><br /> <br /> But great job on putting this together. Great stuff.
hay man thanks for the hint of running the 1 watt overspec.. <br>i have also sinilar led costs .3 USD here ( yes 1/3 rd of a dollar us ) in pakistan.. they say its one watt.. i tried it running at 750mA it was muchg much brifghter but was also very hot .. so i returned back to 350mA usng pot .. so i think if i attach a large number f these to a pc heatsink and attach a 12 volts (1.5 Watt) dc brushless fan it can be very bright as well as cool and give more life ? what r ur words? have u over driven it ? can u share more info ..
when mounting the VREG with a TO220(or similar) casing, how did you manage to get the screw that holds the VREG to the heatsink, not to touch the inside of the hole in the VREG ? I always had this problem, how did you resolve it ?
Hi. Have read all your material with great interest and appreciation. Thank you. Have built your LM1084 circuit many times for LED projects. The lastest is interesting in that I designed a 1.55A array using a 0.4 sense resistor (actually 2 X 0.8 ohm sense resistor in parallel). When I measure the amperage while the circuit is ON the reading is a steady state 600ma and no where near the 1.55A the circuit should draw. Any ideas or suggestions appreciated.<br><br>Thanks again for all the helpful instructables.
I have an idea. Due to changes in the light's enviroment like temperature, time, or weather they change to preset colors. <br><br>ex.<br><br>60 degrees and under bright blue<br><br>Sunny Day Yellow<br><br>Get home from work/school Cyan
I wonder if Q1 getting really hot in a short time is normal. It is similar to the one used in this instructable.
That is normal - hence the big heat sink. The more power the regulator dissipates, the more you have to sink.
I am using an LED with these stats:<br>2.9V @ 700mA<br>3.35V @ 3A<br>I want to control it up to the max current. Seems you define R3 for a single current. Do I calculate that with the max (3A) current, giving a 0.2-Ohm resistor (closest value)? Thanks!
I'm wondering, could this potentially be used to "wash" a wall with blue or green while having foreground objects lit with "white" light. The reason I'm asking is this might be used as a "magic" portable blue or green screen for video composting. Yes? No? Maybe? Go to hell?
that should work. i dont see why not. try it, that's the only way to see.
should work, as long as your wall isnt too reflective
im pretty positive that wouldn't work at all.... good idea though, and companies like datavideo actually sell chroma key kits that work with a retro-reflective screen and a ring of green/blue leds around the camera lens<br /> <br /> <a href="http://Datavideo CKL-200 Dual-Color Chromakey Light System" rel="nofollow">Datavideo CKL-200 Dual-Color Chromakey Light System</a><br /> <h1 class="irregualrHeader">&nbsp;</h1> <br /> <br /> <br />
They sell thermal epoxy specifically for heatsinks.. a lot better than silicone. In fact, that's what the reefer led supply shops recommend if you don't drill and screw the stars down. &quot;Arctic Silver Premium Thermal Adhesive&quot;.
Hey, having a little trouble getting this to work right. Mostly it seems the resistor combinations I use won't turn off the LEDs(voltage not low enough) and won't turn them up high enough. I'm using LED's with FV of 3.2 and max of 3.75. Using a 2k pot. 19.5v supply. The LM1084IT-ADJ. What should my R1 and R2 be? Thanks!
Never-mind, I figured it out. Ended up with R1=680, R2=2.7k. I had blown the regulator chip earlier experimenting and didn't realize it! :) Dropped in a new one and presto! Thanks, this circuit deserves grand kudos!
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Great instructable!! I really like it, but there is one question that comes to my mind.<br /> <br /> Lets say i have a power source V and a luxeon Led, and Resistor(R1) in between that makes the led shine in full power.<br /> and now i insert in between a pot meter in series, This would change the resistance of the circuit lowering the current, meaning making the led give off less light, never allowing to go above the R1 value which is the max.<br /> now do this three times for RGB and you got the same project with simpler circuitry don't you? why wouldn't that be good?<br /> <br /> why do you choose to use voltage regulator and transistors?<br /> &nbsp;<br /> This is my only question before i start making this instructable so could someone please explain this in detail to me? Thanks
Because the potentiometer would start smouldering and eventually fail completely. <br><br>Say the current flowing through each LED is 700mA (0.7A) which is quite common for high powered LED's. Now, if the voltage across the LED is 3.2V (full brightness), the the power being dissipated is: P=IV = 0.7*3.2 = 2.24W. If you connected a potentiometer in series with this LED then it would also have to be capable of dissipating this much power. However, most pots have an absolute maximum power rating of 0.5W which is well below what is necessary, which is why it starts smouldering. <br><br>Using the voltage regulator, the current on the input branch (the one with all of the resistors in it) is kept very low and therefore the power dissipated by each resistor is very low. But, the current in the output side can be SET (using R3) to anywhere up to 3 or 5A depending upon what voltage regulator you use.
Hello! This project is amazing - I would like to make it for some friends of mine that just got married and a house. They built their own bath tub, which is amazing in itself. Now, they would like to have some rgb LED's to light the tub romantically and who am I not to provide? But I would like to offer them some dynamics and a remote. I have found the following product:<br><br>http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&amp;Page2Disp=/specs/LDRF-RGB4.htm<br><br>but I am not quite happy since the analog driver that makes this project so beautiful is not included, which is neigh impossible with a remote I imagine. Anyway, do you have any advice for me? Thanks in advance!
I just finished making my own rgba light (yes it has amber as well !) You can see it <a href="http://www.candlepowerforums.com/vb/showthread.php?t=286602">here</a>.&nbsp; It puts out over 2400 lumens at 80watts! Thank you Dan for the best instructable ever!
is very exelent, and veri prolijed
I've been using the more &quot;simple&quot; current driver with NFET, NPN, and R1&amp;R2, and it has work great for 1watt, 3 watt and 10 watt LEDs.<br /> I'd like to construct the controllable driver with voltage regulator for use with (2) 10 watt LEDs; V= 23 volts, current = 1000ma. Cut off voltage =18 volts, max voltage= 23 volts. I'll use the 2.5K pot for R4. I need to figure values for R1&amp;R2, but I am math/calculation deficient ,Any help will be appreciated.<br />
Hi, id like to know how you cut your board. Like what tool did you use? thanks.
Looks like there's a hacksaw in that photo. That's likely what he used.<br />
&nbsp;I found this controller shield for the arduino. Does anyone&nbsp;know&nbsp;that, if properly combined with this instructables controller, it could be used to control the system. it has 10 K&nbsp;potentiometers&nbsp;and other&nbsp;useful&nbsp;inputs and&nbsp;controls&nbsp;. i figure that if the programing was done right, it would make an&nbsp;excellent&nbsp;controller module. please&nbsp;respond&nbsp;ASAP and give me advice.<br /> <br /> <a href="http://www.sparkfun.com/commerce/product_info.php?products_id=9597" rel="nofollow">www.sparkfun.com/commerce/product_info.php</a><br />
Here you can see my assembly. It cost me about $200 here in Latvia.<br /> Used single 10W led for each colour. Also I used potentiometers with switch, so I can turn off each chanel completely without the VREG burning. The hardest part in all this was getting the right R1 and R2 and insulating the VREG.<br />
forgot to say thanks to Dan :)<br /> excellent instructable<br />
For 1W LED's, would 80 degree C wire be safe enough to use?
Thank you for all the responses!
Has anybody found a new website that sells these LED's. It seems that the links he posted are now dead.
ebay is usually the cheapest.
What I was saying before I deleted my own comment was:<br/><br/>Three Things:<br/><br/>1. The link <a rel="nofollow" href="http://www.lumiledsfuture.com/">http://www.lumiledsfuture.com/</a> is outdated, you should remove it.<br/>2. The other link <a rel="nofollow" href="http://www.futurecb.com/">http://www.futurecb.com/</a> works fine, but<br/>3. In the FutureCB link, there is a parenthesis at the end of the link, making it so you can't directly access the site from the link. You should edit the link so the parenthesis isn't messing up the link.<br/>
Oh yeah you should also replace LumiLEDsFuture with FutureElectronics.com
will a different type of npn transistor work, not many a stores sell them, and cbf ordering one
I've got everything I need for this project but my potentiometers/sliders are slightly different in terms of the legs, it has five pins on each side. Attached is a diagram and some pictures (sorry bad quality). Can you please help. Tell me which leg goes to which wire. Thanks
I would say the extreme corner pins are mounting pins to create a reinforced attachment to the circuit board and the two clusters of three pins are for TWO separate potentiometer tracks. Possible from a stereo system or something.
As a matter of fact you are right, I went to my electronics teacher and he wasn't too sure either so we used his multimeter and worked out that it didn't matter which side you would solder because it gives the same output. The very outer pins are for mounting, the single inner pins are the input and the two inner pins are the variable output. Its like on a circular potentiometer it has three pins and two are the variable output. My teacher said that if you solder them together it will give you both low and high variables of resistance.
Do you own a Multimeter ? Is there any text printed on the potentiometers ? If there is text google the text plus datasheet and probably you will find more.
I do not own a multimeter, it says: B10KX2 - but that is just the model number. Any ideas?
I recommend you to buy a Multimeter if you want to do more electronic-stuff. But you can build the whole circuit and connect the wires to the potentiometer in every possible configuration. This should be no problem cause every multimeter can have the value zero.
Ok, thanks - what does a multi meter do anyways? Sorry I'm not so smart in electronics but I want to be. lol.

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Bio: Dan Goldwater is a co-founder of Instructables. Currently he operates MonkeyLectric where he develops revolutionary bike lighting products. He also writes a DIY column for ... More »
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