Comment by jwr | Hacker News Reader

Comment by jwr | Hacker News Reader

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We are still in the dark ages, though. Just consider: this "bulb" has to plug into the standard 110/230V AC electrical sockets. Powering an LED is nothing like powering an incandescent bulb: you need a constant current driver delivering a precisely measured DC current that, depending on the LED, is between 300mA and (say) 1.5A. The voltage you need depends on the number of LEDs in series, but assume 3.2V per LED. If you want dimming, you need to do PWM (pulse-width modulation).

This means that inside every "bulb" like this there is a small switching power supply. And small switching power supplies that can take you from 110/230V AC to 3-24V DC are a) expensive, b) not very efficient.

Even more amusing is the "dimmable" bulb: traditional dimmers in AC circuits use triacs to effectively cut out (e.g. cut to zero) a part of the sinusoidal AC waveform. Meaning you get a chopped-up sine waveform behind the dimmer. Any switching PSU won't really notice, as long as there is enough (let's use a technical term) "oomph" left in the waveform. So, what the "dimmable" solutions do, is look at the AC waveform coming in, notice that it isn't really a sine and a part of it has been cut out, estimate how much has been cut out, and provide a PWM dimming signal to the LED driver.

Sure, it's all still better than the incandescent bulb, but it's very costly and inefficient. It also generates a lot of waste: if you throw out an incandescent bulb, it's really just some glass and a little metal. The LED "bulb" contains at least 20 electronic components and a PCB apart from the LED itself.

I think that sooner or later we will need an additional electrical standard, 24 or 48V DC with an overlaid control signal for dimming and a new standard for sockets. 110/230V simply doesn't make sense for powering single bulbs anymore.

How about power over Ethernet? I'm only half-joking here.

If Wikipedia is to be believed, you can get 14 watts from some implementations, 25 from others, and supposedly up to 51 from still others. That seems like more than enough for these new bulbs. I think the last CFL I bought from Ikea was in the neighborhood of 15 watts.

The control interface would hopefully evolve naturally from this. :-)

(Also, bonus points for figuring out how to make all of your light bulbs into boosters for your wireless network. They're already in all the places where people go in a house.)

Unfortunately PoE as currently implemented is probably not the solution, as there's a non-negligible amount of power lost along the thin wires in a Cat5e cable and in the power converters at each end.

How much power is lost with all of those dumb little DC bricks all over the place right now?

With PoE you lose the power three times instead of just once. You have an AC-to-DC brick for the PoE injector (or similar inside of a PoE-enabled switch), then resistive loss on the cable (about 2.4W lost for every 12.5W that reaches the device[0]), then another DC-to-DC converter at the device itself.

Now, don't get me wrong. I really like PoE, and would love to have something similar for lighting, but PoE itself can't handle the current required for primary lighting.

How much power is lost with all of those dumb little DC bricks all over the place right now?

According to http://what-if.xkcd.com/35/, as a rule of thumb, any DC transformer that's not warm to the touch is wasting less than a penny of electricity per day, and a cellphone charger, if not warm to the touch, less than a penny per year.

[0] http://www.connect802.com/ethernet.htm

24 (or 48) volts is still too high - so you would anyway need a power supply.

And go too low on the voltage and the wires become so large as to be impractical.

These types of smart active electronics are getting cheaper and cheaper. I really don't see much need to eliminate them.

24V is just fine for a string of up to 6 LEDs. Your comment leads me to think you haven't designed many switching regulators. You can drive up to six LEDs from 24V at 92% efficiency with 6 components (I have a device I've designed in front of me that proves it): one IC, an inductor, a resistor, a diode and two tiny capacitors.

I agree that we need a closed-circuit DC solution for households. One efficient step-down, and then we plug rechargeable (phones, laptops, etc) in, and power LED lights off it. We still need AC to transmit power to the house, and power high-juice devices, obviously.

Presumably this already exists? Any home-hackers know who's making them?

The off-the-grid folks are surely on top of this. They also have the advantage of a 'natively' DC supply coming off storage batteries.

Use boat lights.

> if you throw out an incandescent bulb, it's really just some glass and a little metal

Actually, one of those metals is lead (Pb), which is highly toxic, so be sure to recycle your incandescents! If nothing else, to lower crime rates...

http://www.economist.com/blogs/theworldin2013/2013/01/lead-a...

The amount of lead in an incandescent light bulb is absolutely minuscule - if there is any there at all.

I doubt there are any facilities at all that try to separate out the lead. All the metal is just melted together and the lead (if any) is diluted among it.

can the switching power supply and other electronics not be combined into a part the screws into the light bulb socket, into which the 'bulb' part attaches? That way in 10 years when your light burns out you wouldn't replace the base part anyway, just the LED lights.

Problem is that the driver electronics need to be tuned to the LEDs being used. So you can't mix and match the LEDs and drivers without some adjustment.

Another problem is the lifetime of the driver electronics is limited too. So the benefits of having separately replaceable driver would be fairly limited.

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