riddle me this....we all know that the LED's use DC voltage to operate, and household current is AC. You will have to have some sort of step down transformer to drop the AC from 120 (USA) volts to 12-24 volts AC, then rectify the voltage to DC. Isn't the step down transformer going to "waste" electricity? I hear stories about environmentalist telling people to unplug the "bricks" when you aren't actively using them. Yes, a bulb will have the step down inside the bulb enclosure, and would be disconnected when the light socket is off, but when on, isn't the transformer wasting "juice" in the step down process?
First, rectifying an AC signal to full DC is not hard at all, just 4 diodes and you're done. Especially when talking about diodes, as they are not sensitive to non-uniform signals (you don't need a filter).
Second, depending on the LED voltage drop, you technically do not need a transformer at all. Granted, it can get stupid sometimes, but if you had an LED with a 3V drop, then if you wired 40 in parallel 40*3=120V. Bingo, no transformer needed.
Also, technically, you don't need a rectifier either, depending on the LED response time. You might be able to see the 60hz flicker out of the corner of your eye, but probably not.
Have you ever used LED christmas.... er I mean "Holiday" lights that use LEDs. No rectifier that I can spot, and definitely no capacitor to smooth things out. If you move those things at all the 60 Hz flicker becomes nauseatingly apparent.
Not as much energy as an incandescent bulb wastes to heat. The average incandescent bulb uses 60 watts. An equivalent compact fluorescent lamp uses about 14 watts. A Macbook with adapter uses 16.6 watts when idling with display on. A current technology LED bulb that is equivalent to a 70 watt incandescent uses 9 watts (although the light won't behave the same way as CFL or incandescent light, so depends on the application). The amount of power loss in the DC conversion is pretty minimal, compared to the potential energy savings of using LEDs instead of CFL, that is of course assuming they can make the technology better within the next few years.
unplugging unused wallwarts/surge protectors for environmental reasons is utter crap.
in ideal theory, a transformer does not consume energy and only converts energy. in the non-ideal and realistic world, transformers operate with >95% efficiency and emit only a tiny amount of heat compared to the amount of power they convert. if nothing is even consuming power, a realistic real-world transformer consumes only a small fraction of a watt.
just to show you the math, if a plugged but unused wallwart is emitting 0.5W of heat (a very realistic number), unplugging the wallwart for 24 hours saves the same amount of energy as an average single electric stove plate consumes in 30 seconds, or that a car consumes in less than a second.
hence, don't be penny-wise and pound-foolish; there are better ways to save energy than unplugging wallwarts.
dv.. you do the math only 0.5W you say? that's per brick, so assuming only half the population of NZ has cell phones and they all leave the brick in the socket cause hey, what's half a watt per day, and that's like 2,000,000 people. so we're only wasting 1,000,000 W per day... peanuts
Reader Comments (Page 1 of 1)
Rusty @ Sep 26th 2007 4:10PM
riddle me this....we all know that the LED's use DC voltage to operate, and household current is AC. You will have to have some sort of step down transformer to drop the AC from 120 (USA) volts to 12-24 volts AC, then rectify the voltage to DC. Isn't the step down transformer going to "waste" electricity? I hear stories about environmentalist telling people to unplug the "bricks" when you aren't actively using them.
Yes, a bulb will have the step down inside the bulb enclosure, and would be disconnected when the light socket is off, but when on, isn't the transformer wasting "juice" in the step down process?
staniel @ Sep 26th 2007 4:17PM
First, rectifying an AC signal to full DC is not hard at all, just 4 diodes and you're done. Especially when talking about diodes, as they are not sensitive to non-uniform signals (you don't need a filter).
Second, depending on the LED voltage drop, you technically do not need a transformer at all. Granted, it can get stupid sometimes, but if you had an LED with a 3V drop, then if you wired 40 in parallel 40*3=120V. Bingo, no transformer needed.
Also, technically, you don't need a rectifier either, depending on the LED response time. You might be able to see the 60hz flicker out of the corner of your eye, but probably not.
joel @ Sep 26th 2007 4:31PM
Have you ever used LED christmas.... er I mean "Holiday" lights that use LEDs. No rectifier that I can spot, and definitely no capacitor to smooth things out. If you move those things at all the 60 Hz flicker becomes nauseatingly apparent.
iDevin @ Sep 26th 2007 4:32PM
Not as much energy as an incandescent bulb wastes to heat. The average incandescent bulb uses 60 watts. An equivalent compact fluorescent lamp uses about 14 watts. A Macbook with adapter uses 16.6 watts when idling with display on. A current technology LED bulb that is equivalent to a 70 watt incandescent uses 9 watts (although the light won't behave the same way as CFL or incandescent light, so depends on the application). The amount of power loss in the DC conversion is pretty minimal, compared to the potential energy savings of using LEDs instead of CFL, that is of course assuming they can make the technology better within the next few years.
Sources:
http://www.apple.com/environment/resources/specs.html
http://www.treehugger.com/files/2007/02/led_bulb_replac.php
http://en.wikipedia.org/wiki/Compact_fluorescent_lamp
dv @ Sep 26th 2007 5:05PM
unplugging unused wallwarts/surge protectors for environmental reasons is utter crap.
in ideal theory, a transformer does not consume energy and only converts energy. in the non-ideal and realistic world, transformers operate with >95% efficiency and emit only a tiny amount of heat compared to the amount of power they convert. if nothing is even consuming power, a realistic real-world transformer consumes only a small fraction of a watt.
just to show you the math, if a plugged but unused wallwart is emitting 0.5W of heat (a very realistic number), unplugging the wallwart for 24 hours saves the same amount of energy as an average single electric stove plate consumes in 30 seconds, or that a car consumes in less than a second.
hence, don't be penny-wise and pound-foolish; there are better ways to save energy than unplugging wallwarts.
McFly @ Sep 26th 2007 8:22PM
dv.. you do the math
only 0.5W you say? that's per brick, so assuming only half the population of NZ has cell phones and they all leave the brick in the socket cause hey, what's half a watt per day, and that's like 2,000,000 people. so we're only wasting 1,000,000 W per day... peanuts