Technical Question: Power Consumption and Dimmer Switches

[athelind]

I have a technical question for anyone with a better grasp of electrical mumbo-jumbo than Your Obedient Serpent possesses.

I have heard that if you have a light connected to a dimmer switch, turning the dimmer switch down doesn't reduce the power consumption -- it just converts the excess power to waste heat.

This makes as much sense as anything about the mystical forces in the wires does; a dimmer switch is an adjustable resistor, so it reduces the power available to the bulb by keeping the load constant.

On the other claw, I'm rolling poorly on my Google Fu dice; I can't find any references to confirm this, that explicitly state that turning down a dimmer switch doesn't save power in terms clear even to laymen with less grasp of the galvanic arts than mine.

And, devoted readers and honored friends -- if you don't have the Mojo, please refrain from offering responses of the "It seems to me..." and "What I think..." natures. I'm not looking for opinions; this is a field subject to rigorous measurement and mathematical analysis, and I want the facts from Those What Know Their Shit.

Comments

[kfops.livejournal.com]

Definites include that power is indeed turned to heat and why dimmers were usually eschewed in most of our electrical contracts.

I remember there was a lot of safety concern about using dimmer switches with any sort've load.

In fact, I can't recall installing a dimmer switch in any of the new houses that we worked on.

[kfops.livejournal.com]

The of course, I did find this after immediately posting. That durn changing technology: http://www.factsfacts.com/MyHomeRepair/DimmerSwitch.htm

[tombfyre.livejournal.com]

Older dimmer switches used resistors to tone down the power, and did in-fact just convert the extra energy to waste heat. Modern ones however use transistors, and thus let you turn lights on much faster, while actually reducing power consumption if you're dimming the light. This also doesn't produce waste heat in the switch, and reduces the heat of the bulb. 'tis a good idea though to make sure you use a bulb thats meant for a dimmer switch. Some florescent bulbs don't work well or at all in dimmers.

[athelind.livejournal.com]

We've got older ones in our rental house.

We discovered that we have to use incandescent bulbs in them even if we crank them all the way up at all times; they just ream CF bulbs.

It makes me not-happy.

[r-caton.livejournal.com]

Dimmers don't use resistors/rheostats these days (they'd have to be darn chunky beggars to dissipate the energy)
They use triacs to instantaneously cut the voltage to zero at a given point of the alternating voltage cycle (instead of waiting until the voltage passes through the zero point). This cuts the power dissipated (which relates to the area under the curve)but plays hell with fluorescents since when there is no voltage the lamp is out. And as the lamp dims the length of time it is out increases until it gets cold enough inside to need the starter to kick it on every cycle. Normally the starter kicks the lamp on by doubling the voltage across it, and then the temperature of the gas within the bulb keeps the current flowing without the need for the starter or the lamp heaters.
Turn down a fluorescent on a dimmer and you'll soon see when that point occurs!

[foofers.livejournal.com]

Switches are cheap. Perhaps the landlord would allow you to swap them out.

[(Anonymous)]

If you plan to use a zero-crossing dimmer on standard fluorescent lights, you generally need an incandescent lamp to be wired in parallel with the fluorescent to act as a load damping circuit. Even then the dimming is not really all that successful.

There are special fluorescent light fittings that are designed for dimming, but they have internal wiring that is specifically designed to improve the light's dimming capability. From memory, the modified fitting has a dual circuit filament transformer for powering the tube end filaments, which is connected to a feed that bypasses the dimmer circuitry. The tube end filaments remain fully powered whenever the light is on, while the feed from the zero-crossing dimmer controls the potential between the tube end filaments.

[jamesb]

Oopsie ... Forgot to log in first

[tombfyre.livejournal.com]

Yep, the older ones were built with incandescent bulbs in mind, and them alone. :p See if you can get newer ones installed.

[r-caton.livejournal.com]

The tube end filaments remain fully powered whenever the light is on
Sounds like the economy and longevity of fluorescents goes down the wazoo with dimmer switches.

Actually with tungsten filament photographic lights I used to use a Variac (variable transformer)