# two electrical questions **URL:** \ **Category:** Factual Questions\ **Created:** [June 9, 2003, 3:20am UTC](https://boards.straightdope.com/t/two-electrical-questions/180581 "2003-06-09T03:20:53Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![bardos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bardos/32/1069_2.png) [@bardos](https://boards.straightdope.com/u/bardos)\ **Post date:** [June 9, 2003, 3:20am UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/1 "2003-06-09T03:20:53Z")
first one: a dimmer switch, when you have the light dimmed, are you saving electricity or is the same amount being dissipated as heat? second question: the same with a step down transformer from say 220 -\> 110v AC. The transformer is on, but nothing is being used and it’s still hot to the touch, so is it costing money to maintain in this way? thanks, b ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [June 9, 2003, 3:29am UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/2 "2003-06-09T03:29:50Z")
A dimmer switch is basically raising the resistance of the circuit, so overall, less electricity is being used, although some is being burned off in the dimmer. In other words, your total electic usage goes down, but your cost-per-lumen increases slightly. Transformers are constantly drawing a minimum amount of energy when connected the the AC main. This minimum current is call the excitation or magnetizing current, and represents a loss in the transformer’s core. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 9, 2003, 3:41am UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/3 "2003-06-09T03:41:08Z")
> [@](#): > > \*Originally posted by Q.E.D. \* > **A dimmer switch is basically raising the resistance of the circuit, so overall, less electricity is being used, although some is being burned off in the dimmer. In other words, your total electic usage goes down, but your cost-per-lumen increases slightly.** Huh? A dimmer switch works by delaying the turn-on of the light until part-way through each half cycle. It uses a triac as a switch. A triac has a small forward voltage drop, and so does dissipate a small amout of heat. The cost-per-lumen _does_ increase, but that’s because the filament is operating below optimal temperature. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [June 9, 2003, 3:49am UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/4 "2003-06-09T03:49:57Z")
> [@](#): > > \*Originally posted by Desmostylus \* > \*\*Huh? > > A dimmer switch works by delaying the turn-on of the light until part-way through each half cycle. It uses a triac as a switch. A triac has a small forward voltage drop, and so does dissipate a small amout of heat. > > The cost-per-lumen _does_ increase, but that’s because the filament is operating below optimal temperature. \*\* I wasn’t talking about a solid-state SCR-type, I was talking about a resistive type. Sorry for the confusion. ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [June 9, 2003, 2:40pm UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/5 "2003-06-09T14:40:48Z")
> [@](#): > > \*Originally posted by bardos \* > \*\*first one: a dimmer switch, when you have the light dimmed, are you saving electricity or is the same amount being dissipated as heat? > > second question: the same with a step down transformer from say 220 -\> 110v AC. The transformer is on, but nothing is being used and it’s still hot to the touch, so is it costing money to maintain in this way? > > thanks, b \*\* Basically, if something electrical is creating heat (dimmer in use, transformer, etc.) then it is using electricity. ---
**Author:** ![bardos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bardos/32/1069_2.png) [@bardos](https://boards.straightdope.com/u/bardos)\ **Post date:** [June 9, 2003, 4:13pm UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/6 "2003-06-09T16:13:08Z")
\>Basically, if something electrical is creating heat \>(dimmer in use, transformer, etc.) \>then it is using electricity. that’s kind of my question. Ok, I’ll get more specific. A 300 watt halogen bulb in a lamp with a dimmer switch. Let’s say i have it dimmed down really far to just a nice soft light. Equivalent I imagine to a 25 watt bulb (lume-wise). So, how much electricity am I using? Am I using it at the rate of 300 watts per hour? Or less? thanks, b. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [June 9, 2003, 4:43pm UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/7 "2003-06-09T16:43:33Z")
You’ve dimmed it a lot, down from 300 W to _the equivalent light output_ of a 25 W bulb. So the bulb itself is operating pretty inefficiently. It’s probably using 35 or 40 W, let’s say 40 W. The dimmer switch itself would consume about 5 W when the light was running at 300 W, and less than 1 W when the light was running at 40 W. So your total consumption is about 305 W at the higher setting, and about 41 W at the lower setting. ---
**Author:** ![casdave](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@casdave](https://boards.straightdope.com/u/casdave)\ **Post date:** [June 9, 2003, 5:00pm UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/8 "2003-06-09T17:00:41Z")
Dimmers also tend to reduce the maximum voltage available to the lamp. This should not be the case, but, having replaced a few dimmers in my time with normal lightswitches the differance in light is quite noticeable. I have also noticed that folk who use dimmers(on low voltage halogens) seem to replace the bulbs more often than those who use them as fill in lighting such as on kitchen units where the bulb is kept at full brightness. ---
**Author:** ![justwannano](https://avatars.discourse-cdn.com/v4/letter/j/7ab992/32.png) [@justwannano](https://boards.straightdope.com/u/justwannano)\ **Post date:** [June 9, 2003, 5:32pm UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/9 "2003-06-09T17:32:17Z")
Look here for an explanation of how dimmer switches work. > **[How Dimmer Switches Work](https://home.howstuffworks.com/dimmer-switch6.htm)** > > A regular light switch takes care of off and on. A dimmer switch handles off, on and everything in between. Find out more about a dimmer switch. The old style switches use more current than just the light bulb. The new switches use less current but more than the amount necessary to operate the bulb without the dimmer. It can cause premature light bulb failure because of the mechanical damage due to the hum. ---
**Author:** ![bardos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bardos/32/1069_2.png) [@bardos](https://boards.straightdope.com/u/bardos)\ **Post date:** [June 9, 2003, 5:59pm UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/10 "2003-06-09T17:59:50Z")
> [@](#): > > - > > So your total consumption is about 305 W at the higher setting, and about 41 W at the lower setting. \*\* Basically that answers my doubts. I do save on electricity when the light is dimmed by the dimmer switch. thanks, b ---
**Author:** ![panamajack](https://avatars.discourse-cdn.com/v4/letter/p/47e85d/32.png) [@panamajack](https://boards.straightdope.com/u/panamajack)\ **Post date:** [June 9, 2003, 6:05pm UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/11 "2003-06-09T18:05:50Z")
> [@](#): > > \*Originally posted by casdave \* > I have also noticed that folk who use dimmers(on low voltage halogens) seem to replace the bulbs more often than those who use them as fill in lighting such as on kitchen units where the bulb is kept at full brightness. This was alluded to above by **Desmostylus** ; halogen bulbs are intended to be operated at high temperatures. In an incandescent bulb the filament is ‘burning off’ slowly over its lifetime. The effect of the halogen is to maintain the filament, but the reaction needs high temperatures to occur. When operated at temperatures below optimal, one of the key advantages of halogen bulbs - long life - is lost (hence the higher cost). In theory you could run the lamp at full brightness occasionally to repair the filament, but I don’t know how much you’d gain from it. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [June 9, 2003, 6:15pm UTC](https://boards.straightdope.com/t/two-electrical-questions/180581/12 "2003-06-09T18:15:14Z")
**Desmostylus** is correct. To expand a bit… A dimmer switch uses a technique of power control called _phase proportional control_, a.k.a. _phased-fired control_ and _phased-angle control_. (I have used phases-fired controller modules on industrial projects, so I’m somewhat familiar with them.) This technique is a simple, efficient, and accurate method of controlling power to a load. Basically, the controller works by delaying _ **when** _ each half wave is turned on via a series solid state switch (a triac or two back-to-back SCRs). When set to full power, the switch is always “on” and thus passes each half wave in its entirety. When you decrease the power, the switch remains “off” for a period of time during each half wave, then turns “on” sometime before the wave finishes; it remains on until the next half wave, where the process starts over. This reduces the RMS voltage to the load, and thus the average power. But there are inefficiencies. Three that come to mind: 1. The solid-state switch (triac or two back-to-back SCRs) has a voltage drop when it’s “on.” I think it’s usually around 1.5 V RMS. The average power dissipated by the solid-state switch is 1.5\*I, where I is the RMS current in Amps. 2. I’m pretty sure most dimmer switches contain a series choke (i.e. inductor) to roll-off the sharp switching transients. From what I’ve heard, the voltage drop across the choke can be fairly high (2 or 3 V RMS?). 3. The controller circuit dissipates power. I have no idea how much power it dissipates, but I would guess less than 1 Watt. Not only are there inefficiencies, but phase-fired dimmers can create a lot of EMI, especially cheap ones.