Homemade Ceiling Light Fixture with Bridgelux (Pics Included)

[andersonEE]

So last week I built a light fixture for my hallway with a 930lm warm white Bridgelux LED powered by a 15W dimmable driver from Roal Electronics. The new light replaces a 75Watt incandescent bulb in an ugly globe fixture. Here are the Pics:

The opening in the ceiling where the old fixture used to be:

3 Foot length of 1/8" aluminum bar used for heatsinking. You can see the old globe fixture in the top left corner.

One end of the bars I scuffed with sand paper to help with heat dissipation.

A repurposed computer heatsink will be the LED mount. Here it is being prepared for drilling.

I tapped the holes with #4-40 threads.

ArctiClean works great for removing old thermal paste and prepping new surfaces.

And here is the LED, with contacts pre-tinned.

ArcticSilver Ceramique used between the led and heatsink with screws keeping pressure. (Not my first choice, but I had it laying around.)

ArcticAlumina and screws to attach the aluminum bar to the heatsink.

From the Attic, the mounting.

And finally, the control shot with light off.

And with the light on (haven't installed the dimmer switch yet).

And

The warm white is perfect. It seems alot like sunlight. It is also very bright...much brighter than the 75 Watt it replaced. We'll see how bright it is after I install the frosted glass beneath it.
I had tested this LED just with the computer heatsink alone (no bars) and it got very hot after 30 minutes or so. With the vertical bars, it barely gets warm after hours of running.
I still have much to do (frosted glass fixture, sealing around the opening with caulk, dimmer, etc) so I'll post more pics when I'm done. I'll post the electrical characteristics too.

 

[andersonEE]

Reserved for more pics.

 

[Steve K]

Pretty slick! I like the idea of the aluminum strips in the attic to act as the heatsink. What's the plan for mounting the globe? Just RTV it to the aluminum heatsink?

Nice report too!

regards,
Steve K.

 

[egghead2004]

Cool idea!

 

[andersonEE]

@Steve - I'm actually not reusing the globe. The plan is to get a piece of Lexan polycarbonate, frost it with some spray paint, and mount it 1-2" beneath the led.

 

[blasterman]

Painting it will really kill efficiency.

If you have a palm sander, try buffing it until it's opaque.

 

[andersonEE]

I was going to use this frosted spray paint. I tried it on a spare piece of Lexan and it worked pretty good. I think it gives a more uniform look than sanding, but then again I might just need a finer grit of sand paper.

 

[jason 77]

Good job! I just used one of the 930 lumen bridgelux LEDs in a floor lamp retrofit, they are quite bright at full power!

Are you going to install a junction box where you spliced into the mains in the right of the picture above? it is code where I live anyway.....

I bought one of these a while ago for a project similar to yours, haven't gotten around to using it yet though.. might be better than trying to fabricate a frosted cover from plexiglass?

http://www.lightinguniverse.com/products/?tid=328&psku=3029451&af=1658

 

[andersonEE]

Yes, I am going to put the spliced sires into a JB.
That's a good idea about the lens. I'll have to check out what Lowes/ HD have to offer.

 

[hank]

Very nice! Do show us your final picture once all the wiring is tucked well away from that aluminum-faced insulation.
(Yes, in fact, I do believe wire nuts unscrew themselves to try to start fires, but then I live in earthquake country where the little shakes add up over time)

Does the driver have any ventilation, or a shutoff if it gets too hot?
I often put small electronics on long screws with standoffs for air circulation.

Are your aluminum bars anodized or painted, rather than bare polished metal?
Here's why I ask:
http://www.candlepowerforums.com/vb/showpost.php?p=3550140&postcount=49
(I read up on emissivity when re-roofing; picked a high-emissivity "cool roof" -- now our attic temp. on hot days is about 85F, vs. 110F under the old tar roof)

 

[andersonEE]

I had also read that post when I was researching for the heatsink design. However, with all the aluminum on this build, everything stays pretty cool. It is barely warm to the touch. I bet it doesn't get above 45 C (touching right next to the emitter). I would measure it but it is kind of pointless when it is that cool. In the summer months when the attic is hot, I will measure again.

 

[kethd]

Wonderful pics -- Thank You!!!

I bought a "real" 4-40 tap. Did not work out well; makes threaded hole too big-loose for my AL heatsink mounting purposes. AL is soft enough that normal zinc-steel screws can self-tap in proper sized hole, and you end up with a nice tight fit. I bought some 4-40 stainless steel screws I hope to form tapered points on for future efforts...

What are the dimensions of your AL bars? How much did they cost, from where? How many actual watts to your Bridgelux, and what is the actual temp distribution along the bars?

Let us know how pleased you are with the dimmer function. And if the color seems to shift with dimming. Not sure what we prefer -- we are used to incandescent color shift with dimming, so maybe it would seem "unnatural" for that not to happen?

Does the Roal Dimmable LED Driver get warm? Are you able to measure the actual PS efficiency, power factor etc?

 

[andersonEE]

I thought the 4-40 tap worked great...threads felt snug to me. Trick was to use plenty of cutting oil and go slowly back-and-forth (never more than a quarter-turn forward without turning it back).

The aluminum bar I got from Lowes. It is 3'x2"x1/8". I cut mine in half so each side is 1.5 feet. If you keep browsing posts in this forum, you'll see that it is quite popular with fixed lighting projects among CPFers.

I was planning on installing the dimmer switch tonight, so later I'll post some info on driver efficiency at different levels.

 

[andersonEE]

Ok, I installed the dimmer and it is working perfectly. Dimming is steady and proportional over the full range, and no color changing or flickering occurs. I only have a Sony Cybershot Point and shoot camera so the pics don't represent the levels very well. I can adjust the ISO so I put it to the lowest setting and hoped that the automatic max shutter speed wouldn't be able to saturate the pics. Well it worked for the lowest level but everything else pretty much looks the same.

Here is the High setting from the dimmer switch.

And here is the Low setting. This actually looks a little brighter in the pic than it really is.

Here are the electrical characteristics for 3 different levels (low, med, high). I also took measurements before I put the dimmer in to see if there were any losses in the dimmer.

The dimmer switch definitely lowers the efficiency a little. And efficiency drops way down with dimming, but this light does exactly what I want it to do. It gives me a nice 6 Watt night-light in the hallway for my family to find the bathroom at night, and gives great, efficient light during the day replacing the 75 Watt incandescent that used to be there.

We use this light all the time (at least 5 hours per day) because it is in such a heavily trafficked area in the house. Electricity for me is about $0.10 per KWH, and I save about 300 Watthours per day with this new light. So, per year, I am saving about $11 in energy costs alone. Haha, I know that's not much but the led and driver are both rated for >50,000 hours so I will definitely make the money back. Total cost for this project was ~$75 dollars including shipping.

 

[kethd]

Thank you for those measurements!

It looks like the driver efficiency goes down so much when dimmed that if one were determined to have HI/LO selectable brightness AND high efficiency, one would need a very different approach to the driver? (The LED is probably even more efficient at lower driver levels, despite Bridgelux telling us all bets are off at less than half nominal drive current). We might need a whole separate low-current driver and a selector switch for max efficiency in both modes? It sounds like in your application you might be able to live with just a HI/LO switch, instead of an ON/OFF switch... (But these fancy commercial drivers seem so expensive it would seldom make economic sense to complexify things thus.)

I hope you give us an update here after 1,000 and 10,000 hours on how things are working out!

(Thank you for the tip about how to tap 4-40 holes properly -- sounds like it could well have been a case of operator error on my part...)

 

[LED_Thrift]

Really nice work on this project. I think you made good choices on LED & driver and the fixture you designed looks like it will work very well.

...We use this light all the time (at least 5 hours per day) because it is in such a heavily trafficked area in the house. Electricity for me is about $0.10 per KWH, and I save about 300 Watthours per day with this new light. So, per year, I am saving about $11 in energy costs alone...

Not to mention the savings during the summer when you are not air conditioning against the heat of a 75 watt incan.

 

[txg]

did you take these measurements with a cheap standard multimeter? that would explain the bad efficiency with dimming, because the measurement is inaccurate. to measure the ac current, you'll need a true rms multimeter or a scope.

 

[andersonEE]

@txg: Yes I did use a calibrated, true RMS multimeter (Fluke). Those measurements are accurate. I am an electrical engineer so I have access to lots of high quality equipment.

That was a good idea though.

 

[kethd]

If your Fluke is like mine, I don't know any way to measure watts or power factor, just true RMS volts, amps, and then calculating volt-amps... The Kill-a Watts (P3 P4400 Newegg <$20) are nice tools, but too insensitive to be very useful at these kinds of low power levels. They use a current-sensing resistance of about .004 ohms, as I recall. I modded one to be a hundred times as sensitive -- nifty tool, but too much of a nuisance, too easy to exceed 15W by mistake. For my next try, I'm shooting for just x10 sensitivity which should be happy compromise, with 0.1W resolution and useful PF etc readings at low end. (The 1W+ resolution of standard unit makes PF readings meaningless at low end.)

 

[andersonEE]

@kethd: I have a Kill a Watt meter too :twothumbs. Also got mine from Newegg. I'd like to hear more about your modding project (with schematics). Sounds Interesting.

About your watts/power factor concerns...the Roal driver lists it's PF at >0.9 so I'm not really too concerned with it. Yes, I have listed Apparent Power in my calculations, when I am only being charged for Real Power by my utility company. So I might be paying for slightly less power than what I calculated.