Practical LED Lighting for Fun and Profit

Intro: Practical LED Lighting for Fun and Profit

LEDs have finally begun to surpass compact fluorescents (CFLs) in effeciency (lumens per watt) signaling the perfect time to move beyond crappy LED throwie projects to real, practical LED home lighting. This instructable presents a method to make an LED replacement for the low voltage halogen bulb pendant you currently have over your kitchen countertop or island just like everyone else who has watched trading spaces or extreme makeover home edition in the past 10 years.

STEP 1: Gather Your Materials

LEDs have been making big strides in terms of luminous efficiency and cost recently. The current champion in terms of efficiency is the the Philips Luxeon Rebel line of power LEDs. The Rebel is not only tiny at about 3mm by 5mm, it is available in models with >100 lumens per watt. For comparison, typical incandescent bulbs hit the 15 lumens per watt and fluorescents the 75 lumens per watt range. The best source for power LEDs is www.ledsupply.com which sells a variety of LED products for all your LED needs. The item we are interested in here is their "Endor Star" which is a thermally conductive but electrically insulated package with up to 3 Rebel LEDs mounted on it. I used the 3x90 lumens/watt star with 480 lumens of output at 700mA drive. This is pretty much equivalent to a typical 50W halogen bulb that puts out 600 lumens that you might have in your low voltage lighting system. This LED array will cost in the neighborhood of $30 but will last as long as $25 worth of halogen bulbs while using 7W versus 50W for a $50 lifetime operating cost versus $375 operating cost for the halogen.

Besides the LED you will also need a driver circuit. Since the plan is to build an LED replacement for a low voltage lighting bulb, we need a driver that can handle an AC input. Low voltage lighting uses a transformer to reduce the typical 120VAC power to a "low" 12VAC level. www.ledsupply.com conveniently sells an AC capable "buckpuck" that will accept 12VAC input and output a regulated 0-700mA output current for driving strings of LEDs.

So go ahead and shop at LEDsupply or equivalent to get the electronics parts. If you want to be able to dim your LED bulb you will also need a potentiometer. The Endor Star will need to be mounted on a heat sink, such as a section of aluminum angle or channel extrusion. This will require holes to be drilled and tapped as well as screws, heat sink compound, and some wire.

Materials:

1. Power led such as a 3-up Endor Star with 3 Luxeon Rebel 90 lumen LEDs
2. Constant current LED driver with AC input ability such as BuckPuck 03021-A-E-700
3. 1.25" section of aluminum extrusion for heatsink
4. 4-6 screws fro mounting LED to extrusion, 6-32 works great
5. Tap for threading holes for screws, 6-32 tap works great
6. Heat sink compound for mounting LED to heat sink. Since the LED is isolated, you can use a metallic based heat sink paste like molybdenum anti-sieze
7. Some wire to hook everything up
8. Soldering tools and a clue

STEP 2: Build the Heat Sink

The chosen 3 piece Endor Star will dissipate in the neighborhood of 7W of electrical power. Since the Rebel LED is about 15% efficient, 6W of that input power will be dissipated in the form of heat. In addition, the output of the LEDs will decrease with increasing temperature and their lifetime will decease with increased operating temperature. So it is in our best interest to keep them as cool as possible. To do this, we mount the LEDs to a aluminum heat sink.

The pics below show how you should drill a series of holes in your chosen heat sink to match the layout of the LED array detail in the datasheet. Then you will need to tap them to accept mounting screws and test fit screws into them. In my case I used 6-32 screws which I had handy and a tap for. Your mileage may vary.

Prior to mounting your LED you may also want to sand and polish the aluminum surface to improve heat transfer. To do this, start with 400 grit and move up to 600 grit sandpaper before moving to a polishing compound like Mother's aluminum polish. Since these LEDs don't generate that much heat this might be overkill, but it is easy overkill.

STEP 3: Mount the LED and Wire the Driver

The next step is to mount your LED to the heat sink. As you can see from the pic, I only used 4 of the six holes for mounting and used the other two to run the power wires from the driver circuit. This has worked fine since all 6 screws are not needed to maintain good thermal contact with the heat sink. Before screwing down your LED, put a dollop of heat sink compound under the LED star. Since the Endor Star is isolated you can use a metal or dielectric based heat sink compound. I used a nickel-moly based anti-seize grease that I had handy since I couldn't find my syringe of heat sink grease. I have not had problems.

Also you will want to solder wires to your LED driver and LED array. In my case I did not want a dimming option so I left those pins open as directed in thedatasheet. Since this project will be part of a low voltage lighting system with its own light switch I left out any switching capability as well.

With the LED screwed down and everything wired as needed, you can glue the driver circuit to the heat sink as well since it is so small. There is no cooling requirement for the driver but this will make mounting the system easier. See pic.

STEP 4: Replace That Halogen Bulb

With the LED and driver wired up and mounted to the heat sink, you will want to test the bulb. Since the AC capable BuckPuck driver can handle AC and DC inputs, apply a suitable input voltage and observe the brightness. Since you have 3 LEDs in series you will need at least 12V of input to achieve full brightness at 700mA of output since the LEDs will drop 10.2V and the driver needs 2V of headroom. If you have a lower input the output will just be dimmer. If your LED doesn't light, read over the datasheets and double check your wiring.

At this point it would be a good idea to double check that your light fixture is really low voltage. Get out your multimeter and set it for AC and measure the voltage across the lamp terminals with the power on. You should see in the 12-15 VAC range. If you see 120VAC then you will need a supplemental step down transformer to bring the voltage down to the BuckPuck's maximum rated input voltage of 36VAC. You can get one at Home Depot or Radio Shack. Since your LED lighting system will only use around 10W you can get by with a pretty small transformer.

Now that the LED is working, the next and final step is to swap it in place of your low voltage halogen bulb. I simply removed the halogen bulb and tied the LED assembly in place with string in my halogen fixture. The wattage of the LED is low enough that the string won't melt. I also used a clamp to hold the glass shade temporarily up and out of my way while I worked. See pic. Feed your power input wires into the fixture as needed and flip the switch for a test drive.

The pics below show the LED lamp lighting up my kitchen. The pics were taken without a tripod, showing the lighting power of the LED lamp. To my eye the light generated was about 75% of that generated by the 60W halogen it replaced. After about 10 minutes of on-time the LED assembly was pretty warm (~40C) but not hot to the touch.

Comments

[Yonatan24]

How is 15% efficiency efficient? Incandescents are more efficient than that...

Could you have meant 15% inneficient? Then you would still have a mistake in your calculations...

Please correct me if I'm wrong

[jmengel]

https://en.m.wikipedia.org/wiki/Luminous_efficacy

Yes, you are wrong. Thermodynamics is a cruel mistress.

[prithvi.singh.1420]

and don,t know its working and how tostart make it any bady help me

[prithvi.singh.1420]

and don,t know its working and how tostart make it any bady help me

[lancruz]

I just made my first LED lamp. I used 13 3 watt Luxeon Rebel LED's. They are very bright? My question to you is where is the profit. I had fun making, I'm just curious about your thoughts in this direction. Is it the set up for accent lighting that you are speaking of?

[jmengel]

These days, the profit is in reducing your energy bills. Back when I wrote this, the available LED bulbs were pathetic, none of which used the cutting edge high-brightness high efficiency LEDs. You couldn't find a good LED bulb replacement at nearly any price. FYI, the Rebel LEDs are totally old school now, with many better LEDs available (Such as Cree XML). In the meantime, manufacturers are now cranking out a large number of LED bulb replacements, some of which are decent. Nothing yet that is a slam dunk, but progress is being made and as prices come down further I fully expect LED to replace CFL and halogen in most applications. Not in the easy bake oven though. The limitation currently is the fixtures. Houses and buildings have legacy fixtures designed for easy replacement of a glass bulb. In the future, LEDs will be built permanently into purpose design fixtures that will look much different than what we are used to. For all practical intents and purposes, the LEDs will never fail so replaceability in most applications is a waste and since the LEDs make up such a sizeable portion of the cost, the fixture rather than the light element will become "disposable". I've moved on to making purpose built custom LED fixtures along these lines since Philips and the like can handle the bulbs. For example, I've done several moped and motorcycle headlights and am building a set of linear LED arrays for low profile closet lighting, and so forth. Commercialization is another story as safety testing is a must. UL listing will be required and the resulting costs have kept me doing one-off work for myself, friends, and family. The future is bright.

[GeekTinker]

"Not the easy bake oven though" - Even the Easy Bake has dumped the light bulb: http://abcnews.go.com/blogs/business/2011/09/easy-bake-oven-loses-light-bulb-gets-20-makeover/

[fretted]

Yea they dumped the light bulb and the ovens don't work very well my sister had one when we were kids with the light bulb they worked great we bought one for my daughter when she was a child i don't think the cake ever baked right not once my wife ended up putting them in the real oven to make the cakes bake that was way before i joined we ended up trashing the easy for a Violin that worked out better anyway lol

[mcarrell]

This article could really use an update. I recently replaced this very same pendant light in my own kitchen with a 4-LED Feit Electric bulb. it is both attractive, and required no modification to install, just screw in place of the conventional bulb or CFL. It's also brighter than a 60W bulb in my opinion. Say good-bye to Mercury!

[jmengel]

Certainly this is an old instructable with LEDs that are no longer state of the art, and I've written new ones that use newer LEDs with higher efficiencies (https://www.instructables.com/id/Improved-high-power-LED-bike-head-light-with-integ/) such as the Cree XP-G line-up. Additionally, I've revamped the pendant light design detailed here with a better heat sink and cheaper driver so that the the total cost is now around $20 with a top of the line XP-G and around 100 lumens per watt. The concepts are the same however: a good heatsink, a constant current driver, and a top of the line LED.

As old as this instructable is, the Feit bulbs that I have seen are still poor performers in comparison. The efficiencies are miserable, at around 40 lumens per watt. This is in line with a bad CFL. The majority of commercial bulbs are not up to snuff yet, especially the cheap no-name ones coming out of China. There are some good bulbs being made by TESS (and sold through FIRST robotics teams) that are approaching 80 lumens per watt using Cree LEDs in a nice package at $20 subsidized by Google, and Philips has a good bulb with similar specs for $40 (http://www.amazon.com/Philips-Ambient-Dimmable-Replacement-Light/dp/B004IUMGV4).

Thanks for reading.

[jmengel]

I forgot, I wrote up the improved bi-pin bulb:

https://www.instructables.com/id/Replace-Low-Voltage-Bi-Pin-Halogens-with-LEDs/

Since then, I have made similar bulbs with the Cree XP-G stars which are significantly brighter at the same power. The pictured bi-pin has a couple thousand hours under its belt of trouble free operation. It is the most used light in the house.

[jmengel]

Yes there are other solutions out there, with more coming every day. The linked $60 bulb is not bright enough for anything but accent lighting (240 lumens) and is less efficient than a CFL which can be bought for $5. My system is pretty pricey too ($45) and not ready for wide use in a home. With ~500 lumens the light is bright enough for a task or reading lamp with a good reflector but not for general lighting. Pumping it up to 500 lumens also decreases the efficiency (~70 lumens per watt) to that of CFLs. When run at max efficiency (~90 lumens per watt) the setup I show will only put out ~300 lumens which is marginal. For now the lamp I put together is just a proof of concept, too expensive and not bright enough for many uses but as efficiencies improve through 120 lumens per watt and costs drop due to mass fab this type of lighting will find more and more application. I am in the process of building the shown LED lamp into a small portable reading light that can be plugged directly into the wall (120VAC). This will be more useful to me than pendant lights. Stay tuned.

[Rusdy]

You'll be glad to know that there is a 120VAC LED now in the market (or 230V for those in the 'other' part of the world)

Unfortunately, I only managed to find one distributor (Farnell) so far: Order code is 1734729 from www.farnell.com

No driver required, literally plug and play. (Oh, must use heatsink of course :) ), so to make LED light bulb is now even easier!!

PS: Just type '230V LED' on the search box of Farnell's website if you can't find it

[jmengel]

Thanks for the tip.  Interesting product.  As far as I can tell these use a built in rectifier of sorts and a current set resistor rather than a constant current driver.  The result is a nicely integrated solution with poor performance and sensitivity to voltage fluctuations.  Looking at the specs and assuming the LED light engine is their top of the line and capable of 100 lumens/watt the integrated drive electronics are cutting the efficiency in half.  The resulting overall performance is ~50 lumens/watt for cool white and ~35 lumens/watt for warm white.  Not very good.  Low part count is attractive, but I'll wait until something a bit more efficient comes along.   CFL's are cheaper and better than these for most applications.

[Rusdy]

 Good point, I was wondering how they do it. I should have known better a diode is a diode (i.e. DC voltage naturally). After looking at the PCB myself (just got it today), I can't see any fancy circuitry on it. It's simply an RC circuit.

I haven't tried how it works in practice. Will probably flicker like my other 'cheap' 230V LED. Looks like cheap LED lighting is just simply not there... yet :)

[Svartalf]

However, having said that all, one should realize that the CFL, while "more efficient", will not last as long as the LED system would, nor does the LED have the mercury that the CFL does. The thing, while more expensive, is cool, fun to do (Heh...we're all part of that "maker" crowd- why else would we be here on Instructables?), and much more green than the CFL is in the big picture sense of it. Nice intro into this insanity the LED junkies have gotten ourselves into... ;-)

[jmengel]

The amount of mercury in a CFL is less than you think. Snopes lists the mercury in a CFL as around 5 mg (link below). The average fish these days has about 1 ppm of mercury. This means that by eating 5 kg of fish, you consume the same amount of mercury as in a typical CFL. I don't know about you but I have eaten a lot more than 5 kg (11 lbs) of fish since the last time I chomped down a whole CFL bulb. Your mileage may vary.

http://www.snopes.com/medical/toxins/cfl.asp

[Svartalf]

The only problem is the number of CFLs and the fact that while snopes is right, it methylates so easily and causes all kinds of cumulative toxins that most people don't think about- in the fish is only part of the problem. :-) Mercury is your friend, contrary to the stories otherwise, yes. CFL's are part of the solution, yes. But, for me, I've already elevated mercury levels from all the amalgam fillings in my mouth- I would rather like to avoid any more exposure to mercury if possible as we just don't know what the trace amount increases would do to things. The thing is, what you have done is liable to outlast most of the CFL designs, does something that a CFL is less able to do, and doesn't expose yourself to any mercury and less phosphor than the CFL would if it got busted. This doesn't even get into the differences between stated lifespan and actual on the CFLs (I've been using CFLs for some 5+ years now in almost every application to avoid heat and power consumption for reasons I won't get into...)- the bulbs flatly don't last as claimed; I'm always changing the things out and most of the ones I'm changing out aren't in 24 hour service settings.

[rj44319]

Hi, I finally got the stuff in the mail and unpacked it. I tested one and it worked. But i am having problems getting the wires soldered to the pads i am using 60/40 solder and a 25 w soldering iron what is wrong?

[jmengel]

I assume you are talking about the solder pads on the LED star? 2 things make soldering to the star board difficult. 1. The circuit board is of a high thermal conductivity design and heat from the iron is quickly drawn away. 2. The solder used on the board is lead-free and of a higher melting temperature. To solder to the star with 60/40 lead solder you need to get the pb-free solder liquid which might take a stronger iron. I find that I need to use my adjustable 60W high power iron, turned up a bit past where I usually use it and a coarser tip to get the joint done right. Using my 60W temperature controlled Weller does not work well since the temp set point is fixed at 60/40 type temps. Using a 25W may not work at all.

Here is the station I use:
http://store.sra-solder.com/product.php/6266/26