nothingugly

I’ve been bashing my brains all day thinking about lighting fixtures. One thought is that lighting fixutres are closer to pure sculpture than anything else I”ve made. They don’t require lots of internal structure (say, to hold up a tabletop, or a seated human), and they have to let light out. That’s really it, in terms of hard requirements. LOTS of options. I’m adding a little bit of lighting porn to this post - stuff that I love. But both of the fixtures that I love aren’t terribly good in terms of actual lighting - they’re quite dim, really. (One is Greene and Greene from the Thorsen house, and one is a 2/3 scale Frank Lloyd Wright replica by Prairie Designs) .

So. The design I’m working on now is something that would work well with the LEDs. This means it needs a heat sink, which is a bit of a blessing. The more constraints there are on design, the easier it is. I’d like to make a round lampshade, and it would be nice if it were semi opaque. To offset all the maple, glass, and metal in my kitchen design, I’d like it to have a warm tone, and round is good. Where the heck can I get a round red glass cylinder? I was going to use bottles; bottle cutters are readily available. But I think the real answer is that I’ll need to re-purpose some glassware. I’ll spray the inside with a translucent white paint (so it’ll reflect white, and only show minimally from a side view). Mount the whole thing around an aluminum disc for a heat sink (more than adequate - a 2 1/4″ diameter sink will support a 4 watt Luxeon K2), devise a support for the whole thing to hang together, and that should do it. Now, I need to find a source for aluminum discs, and hope that the bottle cutter does what I want it to. I’m also a little iffy on the paint - needs to stick to glass, and be thin enough to be translucent. Hmm.

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I mounted them on copper heat sinks with Arctic Silver thermal adhesive. In retrospect, I could have saved a couple bucks and gotten the aluminum based version. The LEDs in question are Luxeon III and Cree warm white xlamp 7090s. The Luxeons put out 80 lumens, and are quite white (see previous entry). Two of the Luxeons, four Crees. Total lumens - about 650, or about a 50 watt bulb’s worth. As you can see from the pictures, it looks like more than that. Note the different color temperatures in the room lighting. The photograph exaggerates this effect, but not by a lot. Note the “sparkle” effect on the glassware. LEDs are placed every ten inches. If I were to do it again, I’d have the first lamp placed right up against the left hand wall (maybe a couple inches out). But I think the spacing is good.

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Is LED lighting mature enough to light my entire house? I’ve been fooling with white LEDs for a while now, and I think the answer is still “no”, but it’s not as “No” as it once was. Here are the issues:

• Cost per lumen
• Quality of light
• Physical restrictions (heat output, size of LED installation)
• Dimmability
• “Bulb” replacement

I’ve been looking at Luxeon and Cree products.

A 100 watt incandescent bulb clocks in at about 1750 lumens. 60 watts is 860 lumens. Currently, the ballsiest led out there that I know of – the Luxeon K2, is 140 lumens. So, it would take about 12 of these guys to make up a 100 watt bulb. At $6 each, plus a 25 watt LED driver at $89, that’s $162. That’s before you build a structure for it. Ouch!

The other issue with white LEDs is color quality. I’ve seen a bunch of them. The worst look pretty bad – when I looked at them, it was easy to see the single color emitters. They look like tiny disco balls – red, green, and blue. The light is white, but it looks… weird. So does the cast light. Regardless of quality, you really don’t want to look at these directly; they may be less bright than a 100 watt bulb, but the light is way more dense. Those 140 lumens are coming out of a chip that’s 2mm on a side – ouch! Spots! And watch out for blue light specials - I don’t know much about the “blue light hazard”, but it sounds kinda…. Bad. Anyhow, I know these guys make my eyes hurt.

Back to color quality. Luxeon offers white, warm white, and neutral white LEDs. They’re specified by color temprature. The higher the number, the bluer the light. Sunlight is surprisingly blue – 6500K. Incandescent light is quite yellow, at 2800K. This is why photographs of incandescent lighting (see the lamp on the right, shining on the clamps) can appear very yellow in photographs. These are 6500K, 4100K, and 3000K respectively. Cree’s Xlamp 7090-XR-WW is a warm white (they only offer a color range of 2600 to 3700, but you can see from the picture that it’s almost pink).

Older white LEDs look worse to me than fluorescent lamps. But these new ones look pretty good. I thought I would have wanted the warmer white colors, but I prefer the sunlight color. Which is good news, because the warm white LEDs typically have 10 to 20 percent less output than the 6500K products.

Heat. Oh, my. The best rule of thumb is one square inch of aluminum heat sink, vented on both sides (ie: not stuck to anything) per watt. So, in addition to costing darn near $200, our hypothetical 100W LED based bulb will need one heck of a heat sink – 36 square inches! I’ll be something smaller if you use copper, and vent it, but it’s still going to be both big and hot.

All that said, it’s pretty clear that clumping all these LEDs together isn’t using the technology. The multiple points of distributed lighting are quite nice, and have the added bonus of adding a lot of sparkle to glassware. Fewer total lumens are required when they’re spread around.

LED drivers - that’s what they call led power supplies. Apparently, LEDs are VERY fussy about what they eat for lunch, and will go home before school is out if they’re not given just what they want. So not only are drivers necessary, they’re bloody expensive. I’ve been using Xitanium drivers. While the LEDs are dimmable, most of the drivers are not. And those that are aren’t “mains dimmable” – they have a separate 10V dimmer circuit. The application is more “set and forget” than daily usage. Only one manufacturer that I could find makes a “mains dimmable” led driver, Lumotech. I haven’t called them yet, but I haven’t been able to find a retail distrubitur on the web. Sadly, this supply maxes out at 700ma, which won’t be enough to drive the most interesting LED, the Luxeon K2, which requires 1.5 amps.

The final issue is that these LEDs are soldered in place. The life span is impressive; MTBF isn’t listed on the data sheets I’ve seen, but they do specify “up to” 100K hours. That’s about a decade. Pretty good – but all things must come to an end. If I build a fixture around these, and 25 years from now I have to find a replacement… well, it’s a fair bet that they won’t be easily found. Also, replacing them means getting into said fixture and unsoldering these guys. That, or building them with some kind of connector. Given the heat sinking requirements, it’s likely that I’ll have to either replace them with the heat sink or chip them off said sink (if I use a thermal adhesive). In any case, I’m starting to think that an LED fixture is either disposable, or will require a complete rebuild every 25 years. I know, it’s a long time. But I’m designing my house to be handicap accessible, and I’m not 40 yet….

Finally, there’s some very cool stuff coming down the wire in a year or two. Cree just fired up a 1000 lumen (!!!) led in their labs. Expect to see it at a Radio Shack near you in, say… 18-36 months. Here’s the article.

Enough. I hope this helped someone. It ate way too much of my time. I’ll have more photos of the installed LEDs when they’re done. Oh, and I’ve included a rad photo of the heat sinks I cut on the scroll saw.

The Led Light http://www.theledlight.com/ is another good source for raw materials. Their site isn’t the best, but they’re quick to ship.

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