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DC vs. AC lighting, etc.

user-1055444 | Posted in General Questions on

Hi there,
I’m planning a large addition of 2 units to turn my duplex into a 4-plex this summer. It’s been in the planning stages for years now, but I’m about ready to pull the trigger at long last. I’m pursuing high energy efficiency along the lines of PH (though I’m prepared to let it go if I deem it not cost effective in the end; so far the numbers makes sense for me). Anyhow, when thinking about the lighting, LED makes great sense as a spec for the whole house. And when one thinks about it, wiring the lighting in DC makes even better sense–theoretically cheaper in many ways, higher efficiency, easy wiring using CAT-5, etc.

I’ve had my eye on a company that provides a system (http://www.lumencache.com/) for some time now. Derek, the owner, claims cost parity with AC (if you factor in a battery backup system to your AC system, which I ordinarily wouldn’t). Let’s face it, though, it’s likely going to cost me more than a typical AC setup since it’s…not typical.

The question: is this a worthwhile road to go down? Yes, it’d be nice to have the possibility to wire up my IoT house using this system, and LED replacements would theoretically be cheaper than screw-ins (10-15yrs down the line). USB charging ports would be easily available around the house. Etc. etc. But maybe it’s just too soon? I’m an early adopter at heart, but I’m also quite prudent… I welcome your thoughts on the matter.

Thanks!

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Jonathan,
    My house is wired for both 12 volts DC and 120 volts AC. I have both DC lighting and AC lighting.

    I have never seen a significant cost saving for DC lamps compared to AC lamps. I understand your argument, but the fact that the market for AC lamps is huge compared to the market for DC lamps tends to drive down the price of AC lamps.

    Stick with AC.

  2. Tim C | | #2

    On paper, DC lighting seems like a great idea. More efficient, save on redundant components, everyone wins. But in practice... even theoretically, there's not actually much potential for savings, and you won't realize most of them. The driver isn't more than 1/3rd the total cost of an LED bulb, and DC wiring doesn't even let you eliminate it entirely, just use one that might be cheaper if economies of scale bear out. The bare LEDs only get efficiencies ~25% higher than the 120v bulbs. LED lighting already drops your lighting cost low enough that such a small improvement won't save you much at all. And you'll lost most of that gain (if not all of it, or more than all of it) in the centralized power converter and the 12v distribution losses.
    And don't count on cheaper replacements down the line, either. The drivers don't have much (if any) better life expectancy that the LEDs themselves, so it's just as likely that you'll be replacing the LED driver in the fixture as you will the LED bulb.

    And don't expect the wiring to be easier or cheaper. You can't run more than 24 watts down Cat5 at 12v (and actually doing that will significantly hurt your efficiency over reasonable wiring distances) - That's just two 60w equivalents. Which means if you want efficiency, every light fixture gets it's own home run cable. IMO running a wad of half a dozen or more Cat5 cables isn't going to be any easier than running 14/2 romex, and it's definitely not significantly cheaper.

    If it's efficiency you're after, centralized conversion from 120 volts AC to 12 volts DC just doesn't make any sense outside of tiny houses.

  3. user-1055444 | | #3

    Thanks--I had a feeling that's what I'd get in response. Especially with new 'smart' bulbs being announced monthly. It's hard to imagine getting a better deal the $15 connected cree bulbs just released (http://creebulb.com/products/standard-a-type/connected-60-watt-replacement-soft-white-led-bulb).

    BTW, perhaps this deserves a separate post, but: I've noticed as I've been dining out when a restaurant has LED lighting, especially on a dimmer. The light, even though it's warm, seems to have a flickering quality to it. Is this a problem inherent with LEDs, or are there already ways to avoid this phenomenon?

    Thanks again.

  4. charlie_sullivan | | #4

    The answer to "is X inherent to LEDs" is usually no, because there is a lot more design flexibility in making an LED bulb than there is in an incandescent bulb. And this is no exception. LEDs can be made to dim beautifully with absolutely no flickering. In practice, having them work well on a dimmer is something of a hit or miss proposition, because the variation in the driver circuits. Both LED bulb manufacturers and dimmer manufacturers publish compatibility lists. And some of the dimmers have adjustments to dial in the compatibility, increasing your chances of getting performance you like.

    Flicker is a somewhat complex topic, because the sensitivity of our vision system to flicker varies drastically with frequency. With a cheap LED system, there is 120 Hz pulsation of light associated with the 60 Hz line frequency. For most people, this is too fast to see, but there are studies linking that pulsation to headaches and eyestrain. Good LED systems eliminate that. But what you are seeing with dimmers is probably lower-frequency variation.

    As for the original question, I agree with the others that sticking with 120 V is a sensible practical choice. It would be a shame to get locked in to a non-standard system when the technology is changing so fast. If in 8 years, there are much better LED bulbs available, they will surely be available for 120 V, but it's not clear what other systems they will be available for.

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