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Low power low voltage lighting

Following on from my last post...

I've been having a hell of a time over the past few weeks trying to figure out how to build a low-voltage, low-power lighting system.

My constraints have been:
  1. It's gotta consume as little power as possible
  2. It has to be easy to use
  3. It has to look good

That still leaves a lot of scope, so I decided to build under-the-counter lighting using one of:
  • High-power LEDs
  • Christmas lights
  • Halogen lights

I considered the pros & cons of each, ie: LEDs consume the least power, but don't typically look that good. Halogens consume less power than regular lights, but still eat a lot more than LEDs. Each christmas light consumes about as much as an LED but provides nowhere near the amount of light. etc. etc.

I was really tempted by LEDs simply because they draw the least power. Unfortunately all the LED lights I've seen in stores look absolutely horrible! They're called cold white but operating table white would be a better way to describe 'em. Even what store attendants call warm white looked terrible. Gives me a headache just thinking about it. And then there's the price... around £40 for a single-LED light in a basic fixture! And the 'drivers' (which I don't need anyway). It all served to put me off.

I'd almost given up on them when I came across a comment by Joe Russack when googling around. On reading through his experiments with LEDs I decided to try something similar.

I found Cree XLamp 7090 XR, Luxeon I and Golden Dragon LEDs at RS Components, an online electronics store I use. At ~£3.50 each, that's a lot cheaper than the lighting stores! Still, I realized I'd have to do extra work (like building heatsinks, and a 'driver') for them which can be expensive, but I would've had to most of that anyway regardless of the solution I chose. So I decided to dive in & buy one of each (I opted for warm white based on what I've read about colour temperature).

Test LEDs

When they arrived I almost blinded myself & Nika trying them out with a few AA batteries... they're definitely bright! I was also encouraged by the quality of the light - it seems to be a lot less cold than the LEDs I've found in lighting stores. Off to a good start!

I soon realized that the Cree XLamp 7090 XR was gonna be difficult to work with because it has no easily solderable terminals (I didn't want to muck about with reflow soldering at this early stage). But the Luxeon I & Golden Dragon were easy enough to work with.

I grabbed the Luxeon I, copied some ideas off Joe and a dozen other people (in particular, VK2TIP's Regulated Power Supply - High Current Page and National Semiconductor's LM1086 spec's application suggestions) and hacked up a prototype. I ended up with something like this.

Luxeon I experiment

Unfortunately I ended up frying the Luxeon I in a blaze of stupidity. But that gave me the opportunity to gain first-hand experience of how well the heatsink epoxy works. *sigh*. When I finally managed to chip it off I was able to replace it with the Golden Dragon.

Golden Dragon experiment

The circuit draws 0.46A at 3.53V, or 1.6W - not too shabby! I've not yet calculated how much the cooling fan and voltage regulator are drawing, but I suspect altogether it'll be nowhere near 10W. To my understanding, if I have several lights in series the regulator should dissipate less power, which is just what I need.

I've ordered some more LEDs (including a Luxeon Star which should be much easier to glue to a heatsink) and will try & string everything together sometime soon. I'm thinking 4 or 5 lights in total.

Once that's done I'll have to figure out how to dissipate the light.

All in all, this is looking quite promising!


Nov. 2nd, 2007 05:22 pm (UTC)
Very cool! I can't believe how much work and thought you've put into this.

Can you get some kind of funky shade/light covering from somewhere like Ikea - to help dissipate the light?
Nov. 2nd, 2007 06:14 pm (UTC)
Yeah, that's what I'm mulling over in the back of me mind. Joe Russack had some luck with candle holders, but as these will be hanging upside down I'm not so sure that'll work. I was thinking a quarter of PVC pipe spray-painted with silver might do the trick... bounce it off the pipe & the wall to diffuse it. But then it may block too much light. We'll see.
Nov. 3rd, 2007 01:43 am (UTC)
Re: shades
What about something like this or like this? The first one is like an upside down candle holder...

Whatever you decide to do, I hope you post some pictures of the finished product. I'm very curious to see what it looks like!

P.S. Did you see that I started a new blog?
Nov. 6th, 2007 12:05 pm (UTC)
Re: shades
Thanks - will put pics will be up once we decide.

Got your new blog on my RSS reader already ;-)