Wiring a house for LED

[Howell]

(no reason to put existing wiring in the conduit, that is for future expansion).

Conduit keeps you from having a screw invade your wiring.

 

[Sol]

I agree with the 4 cat6 runs, that seems about right when you take computers, phones, media players and other devices in to account. I'd probably run some fiber as well. Not that I have any real use for it now, but it seems pretty inevitable so why not do it while it won't cost much more...

I'm totally failing to come up with any reason for the HDMI between rooms though, that ones got me stumped.

 

[Handruin]

When you say you'd run fiber, what kind would you run? I've read other people mentioning this, but aren't there many different types of fiber connectors you could run? Like, SC, LC, single mode, multi mode, TOSLINK, etc. I'm making the assumption it would be something like LC for LAN connectivity, correct?

 

[jtr1962]

Cree will be releasing the XM LED this fall. Assuming that it's priced similar to their other emitters, it should drastically reduce the number of emitters ( and cost ) needed for a given output. Driven at 2 amps, about a dozen of these could light an average-sized room well.

It also bears mentioning that purpose-built LED fixtures are really the best way to go, not screw-base bulbs which have a limited surface area to dissipate heat. All you really need are enough ~4" to 6" wide aluminum channels to run around the perimeter of the room. Stick in an XM LED every foot or so, mount the whole thing in a soffit, add necessary circuitry, and voila, indirect LED room lighting which should probably last for decades. I might add a little red for improved color rendering but the idea remains the same. Going the DIY route should be a lot cheaper this fall than it was when this thread was started.

And you might as well put in low-voltage wiring just in case. I'm thinking if you ever want to install solar panels, you can use it to directly power devices from the panels via the low-voltage wiring, rather than wasting power inverting it to 120 VAC. The only question is what to settle on for the voltage. 48VDC is about the limit before most electrical codes consider the wiring high-voltage. I already mentioned this when I first posted in this thread, but it bears repeating.

The hard part is making electronics which can run off 120 VAC and possibly interface to a dimmer switch ( or perhaps some sort of custom dimmer ). It's somewhat easier if you start off with 48VDC or less.

 

[ddrueding]

I had thought of installing a large-ish transformer, and having a low-voltage DC run for general lighting. I knew 12v would have too much drop-off, but I hadn't considered 48v (I was thinking 24v).

The question is, is it possible to run normal-ish wiring while accomplishing this task? If I were to put the transformer near the circuit breaker, and wire the DC channels to code with 12-3 Romex, than they could be converted back to 120v AC if I decided to sell.

Also, how tricky is it to convert the 48v DC to 12v DC for fixtures?

 

[jtr1962]

The question is, is it possible to run normal-ish wiring while accomplishing this task? If I were to put the transformer near the circuit breaker, and wire the DC channels to code with 12-3 Romex, than they could be converted back to 120v AC if I decided to sell.

You could run wiring to 120VAC code and just use it for low voltage by connecting to a transformer or power supply. Romex will work just fine for that actually.

Also, how tricky is it to convert the 48v DC to 12v DC for fixtures?

Not hard at all. I have a driver that can do it with about 8 parts ( and a few more if you want a dimming control ). Actually, what you would be doing is taking the 48VDC and feeding it to a constant current driver driving a string of LEDs. For 48VDC you could have maybe a dozen LEDs per driver. There's no need to convert the 48VDC to 12VDC. The fixtures you use could be designed to work right off 48 VDC ( or 24 VDC should you decide to use that instead ). 12-3 should be able to carry at least 20 amps. Even at 24 VDC that's 480 watts-plenty to light up several rooms decently with LEDs.

 

[ddrueding]

Sounds very interesting.

Now another question. The ceiling will have significant amounts of insulation. I know LEDs need to be kept cool. If there were two feet of insulation directly on top of the fixture, and I only wanted the emitter exposed below, how would I cool it?

First thought is a water loop, but there might be a simpler solution.

 

[jtr1962]

What I might do in that case is mount the LED on a piece of aluminium plate, mount the aluminium plate flush with the ceiling, and then paint it to match. The paint probably wouldn't act as much of an insulator. The problem would be getting paint to stick well to the aluminium.

Another solution is to have an open space with no insulation right about the heat sink. Think along the lines of a small air duct, perhaps 5"x5". You can have a very low air flow in this duct with a small fan. Or to be honest, natural convection might be enough. The good thing is we're not talking much heat, probably no more than 6 watts input power per linear foot ( and of that 6 watts, about 2 watts comes out as light, meaning only 4 watts per foot of waste heat ). Not a huge heat dissipation problem, and it certainly wouldn't need liquid cooling. The beauty is you have surface area on your side.

Another factor depending upon how long you wait to do this is LED efficiency will continue to increase. Obviously an LED which converts 100% of input power to light won't even need a heat sink. Of course, we'll never get there, but I think >50% conversion efficiency isn't far off. The aforementioned XM LED will do 160 lm/W at 350 mA. That's about 50% conversion efficiency, although in the interests of cost effectiveness it makes more sense to run the LED at higher currents where efficiency is less. However, even at 2 amps this LED should manage >30% conversion efficiency.

 

[ddrueding]

What temperature should I be keeping these LEDs at? Perhaps a "mast" of copper or aluminum to a "sail" above the insulation?

 

[jtr1962]

What temperature should I be keeping these LEDs at? Perhaps a "mast" of copper or aluminum to a "sail" above the insulation?

For longest life you should aim for a junction temperature of 60°C or less. How hot the heat sink should be to maintain that depends upon which LEDs you use, and what current you run them at. For example, the XM LED has a junction-to-case thermal resistance of 2°C/W. If you run them at 2 amps, that's ~6.8 watts per LED. About 2 watts comes out as light, leaving 4.8 watts of heat. That's a temperature rise of 4.8 * 2 = 9.6°C above the heat sink. So for the XM LED at 2 amps, you would need to keep the heat sink at around 50°C in order to keep junction temperature at 60°C.

Note that the 60°C figure is for longest life ( on the order of 100K to 200K hours, if not more ). If 50K hours is acceptable, you can run the LEDs perhaps 20°C warmer.

This paper gives some graphs of LED life versus drive current and junction temperature for Cree X-lamp LEDs.

 

[ddrueding]

Thanks for the info JTR, I'll evaluate the mast/sail idea; better than having a hole in the insulation.

One of the stranger ideas I'm playing with for the whole house is using water to collect the heat from various sources and direct it either into or out of the house via two radiators and a valve. Combining the waste heat from the computers, refrigerator, light sources, maybe even some AV components could allow me to redirect 500W+ of energy to assist in heating or cooling.

 

[jtr1962]

If you use heat pipes for the mast, then your sail/mast idea would work very well. Heat pipes conduct heat hundreds of times better than copper. They would get the heat from the LED source to the sail with minimal temperature rise. Once up in the attic, the sail could be arbitrarily large to dissipate heat as need. The whole idea may even be patentable/marketable, who knows? The big problem is finding a readily available source of heat pipes. I've wanted to play with them for a long time, but haven't really found any distributors like Mouser selling them.

 

[time]

The ceiling will have significant amounts of insulation. I know LEDs need to be kept cool. If there were two feet of insulation directly on top of the fixture, and I only wanted the emitter exposed below, how would I cool it?

First thought is a water loop, but there might be a simpler solution.

Use a tiny fan / large heatsink and vent it into the living space - it's only 6W ...

In Winter, even tiny gaps - let alone heat pipes - seriously degrade ceiling insulation performance. It's better not to have them at all.

 

[Bozo]

On warm days with the sun beating down on the roof, attic temperatures can rise above 100F. Even with forced ventalation it could be hard to get the temperature below 90F.

If you want to paint aluminum, clean it with soap and water, dry, and then wipe it down with vinegar. The acid in the vinegar will etch the aluminum allowing the paint to adhere better.

 

[ddrueding]

I agree, any technique that sends that heat from in the insulated envelope to the outside in an uncontrolled fashion is a leak.

At the same time, even if it is only 6W per LED, that would be 72W for the 12 in the bedroom and 288W for the 48 in the great room. Being able to selectively include that heat in the winter and exclude it during the summer would be a significant asset to a house as well insulated as this one will be.

 

[Sol]

I agree, any technique that sends that heat from in the insulated envelope to the outside in an uncontrolled fashion is a leak.

At the same time, even if it is only 6W per LED, that would be 72W for the 12 in the bedroom and 288W for the 48 in the great room. Being able to selectively include that heat in the winter and exclude it during the summer would be a significant asset to a house as well insulated as this one will be.

You could reroute the cold water pipe that goes to the hot water system through the roof, first use it to cool the leds and then run it through a solar hot water system before dumping it in the heater. Super efficient.

You could even extend the idea to your PC and build a heat exchanger on to your existing water cooling rig. You may occasionally have to take a break from gaming to go have a hot shower or do some washing up though, especially on warm days.

 

[ddrueding]

You could reroute the cold water pipe that goes to the hot water system through the roof, first use it to cool the leds and then run it through a solar hot water system before dumping it in the heater. Super efficient.

You could even extend the idea to your PC and build a heat exchanger on to your existing water cooling rig. You may occasionally have to take a break from gaming to go have a hot shower or do some washing up though, especially on warm days.

That is the direction I was thinking. My wife wants a pool, putting a heat exchanger at the bottom of that would be effective.

 

[ddrueding]

It is time for me to begin wiring and purchasing fixtures.

Unfortunately, the budget for the fancy lighting got sunk into other aspects of the house, so it will need to be fairly normal to start.

Looks like we'll be installing about 50 recessed lights throughout the house.

It seems that even "low voltage" cans each have their own transformer, and accept line voltage to the unit? What are the efficiency gains by running low voltage in this configuration over straight 120V fixtures?

I like the smaller aperture of the 4" cans, but it looks like they max out at 40W bulbs while the 5" cans do 75W and cost nearly the same. Can't afford pretty with that price difference.

 

[time]

You really don't want to go down the halogen downlight path. It's highly inefficient, the bulbs are short-lived unless you buy the really expensive ones, and you have to clear insulation above and around each light fitting.

Halogens are good for accent lighting. Otherwise, they suck.

 

[ddrueding]

You really don't want to go down the halogen downlight path. It's highly inefficient, the bulbs are short-lived unless you buy the really expensive ones, and you have to clear insulation above and around each light fitting.

Halogens are good for accent lighting. Otherwise, they suck.

Thanks for the tip. What should I be looking at? They offer LED lighting, but it is 3200K, ~80CRI, dim, and crazy expensive.

 

[time]

I can't point you to an exact product, but here's what I've found.

GU10 CFL downlights (i.e. mains voltage halogen equivalent) are fairly inefficient. I'm okay with mine, but they only have to throw 1.5m onto a bench, and the reflector bulbs are augmented with multi-faceted conical reflectors. Even then, I sweat on the relative efficiencies of different brands.

My electrician cousin wants me to use side-mounted CFL cans - similar to industrial CFL downlights - but I'm unconvinced. Yes, you can use big-ass CFL bulbs to get them bright enough, but they rely on a lossy diffuser to get a decent result. And CFLs are increasingly spiral rather than folded tube, so the light output to the side is not as pronounced.

A big complaint I have with the industrial versions is that they use cylindrical reflectors, which cause a lot of splash (and glare) out to the sides. You really want them to be conical (parabolic is a bit much to ask for), or just paint them black like a traditional can.

I've seen pictures of standard ES fittings with a conical reflector (white is okay, BTW). With a compact spiral CFL, I'd expect this to outperform anything else short of actual halogen. So that's what I'd suggest in lieu of affordable LED alternatives.

 

[time]

Erm, that wasn't as clear as it could have been. Of course it will out-perform halogen in overall light output - by miles in fact - but you're still talking broad beam dispersion unless you also use reflector bulbs, which takes you back to the limitations of GU10 solutions (light is lost within the bulb and what's remaining has to make it out through a small aperture).

To show I'm not just pulling this out of my ass, I have experimented with a mini-spiral centered in a very large faceted reflector. The resulting forward efficiency is pretty high, but I'm not sure you want 12" diameter downlights ...

 

[time]

This sort of thing is what I mean, eg:

I strongly recommend trying one or two first.

 

[ddrueding]

From what I understand, CFL means not dimmable? I consider that a must-have for domestic lighting, particularly in multi-purpose rooms and bedrooms, which is all I have.

 

[time]

Only those CFL specifically designed for dimmers can be dimmed. Some can't be dimmed beyond 20%, but the main problem is that they're hugely expensive -you're probably halfway to an LED lamp.

Switching lights in banks is a good alternative solution that also keeps the price down.

 

[ddrueding]

Switching lights in banks works, and I actually like the effect, but it means having considerably more lights/fixtures.

 

[time]

Sorry, it's the best I can come up with using affordable products that are available now.

I suppose 40 dimmable lamps at about $20-30 each isn't that bad ... provided you can get them in 4000K. Not as elegant as LEDs, but probably a more realistic option in 2010.

 

[timwhit]

My condo is full of recessed cans. I kept the incandescent lights wherever I wanted a dimmer and everywhere else I got cheap CFLs from Home Depot.

I'm not sure I really like recessed cans. The light is very direct and hurts my eyes. Especially laying in bed with the lights on (even dimmed) is annoying.

 

[ddrueding]

My condo is full of recessed cans. I kept the incandescent lights wherever I wanted a dimmer and everywhere else I got cheap CFLs from Home Depot.

I'm not sure I really like recessed cans. The light is very direct and hurts my eyes. Especially laying in bed with the lights on (even dimmed) is annoying.

Indeed. My design so far is to light stuff I want to look at or use reflections. The Bedroom has lights directed into the closets, highlighting the doors, and wall washers above the headboard; no bulbs visible from bed. In the seating area, the lights are above the coffee table, not the couches.

 

[Bozo]

Maybe you can find some thing here.

 

[ddrueding]

There is some good stuff there, Bozo. They have a PAR30 compatible bulb which uses 132 LEDs to provide the light equivalent to a 50W incandescent while only drawing 6W! While costing 10x as much and only having a 10,000 hour lifespan (likely optimistic).

And there spectral graphs are nothing to be proud of.

I'm looking forward to LED general lighting, but it just isn't there yet.

 

[Stereodude]

They're likely garbage...

 

[jtr1962]

If you didn't have dimming requirements I would suggest flush mount T8 fixtures. Tubes are cheap, readily available in all color temperatures, available in high-CRI, and very efficient. The light distribution is uniform without the harseness of cans. The only downside is dimming in not readily available. They do in fact make dimming ballasts and special control switches. Unfortunately these are all pricey.

As for LED not being there yet, true if you're looking for off-the-shelf stuff but not true if you go the DIY route. Even so, going the DIY route is still pricey compared to something like T8s, although possibly still cost-effective long-term when you consider the longevity and possible energy savings. And high-CRI in higher color temperatures isn't readily available, although you can get around that by combining cool white with a small number of red and amber. I'd say LED is about a year or two away from reaching critical mass where price drops dramatically, plus the available selection goes up.

Home Depot is selling Cree can lights for around $50. Unfortunately only in 2700K. I may pick up one and see if I can hack it to ~5000K or higher.

 

[ddrueding]

Let me know how it works, jtr. I'm wiring the house with 12/2 to all the cans in dedicated circuits, so we can switch the source/voltage out later when something becomes available.

 

[time]

I stopped by our equivalent of Home Depot today and found Philips 20W dimmable spiral CFLs for < US$12. Efficacy of 57 lumens per watt, minimum of 5% (1W), which seems okay for most situations.

As I said, lighting on this scale is something you absolutely should trial first.

 

[ddrueding]

I agree time. I have a single 5" can with a 75W incandescent in it, a 3" LED can light, and I'll look for these dimmable CFLs.