The Biggest Thing Since the Light Bulb • Hacker News Board

Re: The Biggest Thing Since the Light Bulb

#141

Post by rachelbythebay » Thu, Mar 07, 2013, 2:39 AM UTC

nitrogen wrote: post #140

rachelbythebay wrote: post #111

Earlier quoted context omitted.

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 fo…

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?

Re: The Biggest Thing Since the Light Bulb

#142

Post by nitrogen » Thu, Mar 07, 2013, 4:10 AM UTC

rachelbythebay wrote: post #141

nitrogen wrote: post #140

Earlier quoted context omitted.

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

Re: The Biggest Thing Since the Light Bulb

#143

Post by Terretta » Thu, Mar 07, 2013, 11:25 AM UTC

tehwalrus wrote: post #82

jwr wrote: post #77

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…

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?

Use boat lights.