Is a dimmer and incandescent light efficient?

[Adam Aglionby]

,

tungsten, halogen or not , is resistive load so power factor shouldn`t come into it

-- Adam

[Thomas Prufer]

Agrees with the figures at:

where it tells all about how much light for how many hours to expect per watt, and per applied voltage...

Thomas Prufer

[The Natural Philosopher]

It probably is. To be honest we seldom DO dim them..although we can..

[The Natural Philosopher]

,

over the voltage range, or even over a complete mains cycle..its heating and cooling noticeably and you can pick up the fluctuations on an optical tacho.

[Martin Bonner]

,

Oh for sure. I was wondering if the dimmer introduced a power factor, rather than reducing current.

[The Natural Philosopher]

,

Sort of..sort of not..

It chops the waveform. So the current is definitely out of phase with the voltage..bein zero some of the time,and in phase the rest.

I'd hesitate to say what that means in terms of power factor though.

That is a term that is applied to liner combinations of L, C and R, which a dimmer most certainly is not.

[meow2222]

And for other figures the equations are here:

the equations section.

Filament lamps are around 2% efficient, but when dimmed this nosedives.

NT

[meow2222]

And for other figures the equations are here:

the equations section.

Filament lamps are around 2% efficient, but when dimmed this nosedives.

NT

PS the energy efficient alternative to dimmers:

[Adam Aglionby]

,

Good point, most dimmers have a choke in line with the load.

Adam

[Andrew Gabriel]

Measurement was Watts, using a true power meter.

The load isn't resistive -- it's a resistance in series with a dimmer, and will have a power factor < 1 due to the dimmer's switching action.

Yes it does.

[Andrew Gabriel]

Also at low levels, filament evaporation reduces. In order to get blackening, you need a lamp geometry such that the filament can still be hot enough to cause significant tunsgten evaporation whilst the bulb wall temperature has dropped below 250C.

I have seen some suggestions that it might, but usually qualified with a comment along the lines of people not being sure if the tungsten can recycle once it has condensed onto the bulb wall.

I've only had this happen once, with a couple of Ring 500W halogens. I suspect a more likely explanation is that there wasn't actually any halogen in the bulb in the first place.

Another cause of this can be a draft which causes the bulb wall to drop below 250C during normal operating.

[David Hansen]

On 06 Mar 2008 16:44:21 GMT someone who may be [e-mail] (Andrew Gabriel) wrote this:-

Interestingly those usual suspects who claim to be very interested in figures have not responded to your figures. I think this tells us all we need to know.

[The Real Doctor]

I thought a dimmer just switched the supply by triggering at different points in the sine wave. In which case, how can it introduce a non- unity (ie voltage and current out of phase) power factor? The load is still - bar a tiny effect from the coiled filament - purely resistive.

Ian

[The Real Doctor]

That's not surprising, really, since the light output voltage relationship for an incandescent bulb is extremely non-linear. Something like (digs in memory) seventh power.

However, I'd like to know how you measured the power in this case. Measurements on very jagged waveforms (ie very high bandwidth) are notoriously tricky to do, as the peddlers of many perpertual motion machines have strenuously resisted finding out.

Ian

[The Real Doctor]

Yes! We used to count David's "Nice try" postings over on uk.railway, but gave up when he got to several hundred, Does he do "Excellent. Personal abuse." here as well?

Bless him.

Ian

[Chris Charles]

Why is the current out ofm phase with the voltage?

The filament is overwhelmingly resitive so the current and votage must be in phase. No voltage = no current however the voltade is applied.

[Chris Charles]

What are you talking about? If you are going on about "usual suspects" why don't you name them instead of trying to appear all knowing.

As far as the figures you copied go why should they be challenged? So far in this topic no one seems to have taken into account that the filament resitance drops if the temperature falls, and as less light output = lower temperature the current will increase. So its possible that a 500w light working at 40w will consume nearly full current. Measurments would show this.

[Huge]

All the time. And very wearisome it is, too.

[Thomas Prufer]

Ah, but this depends on what one wants to do!

One thing to measure accurately for purposes of knowledge, scientific advancement, or the satisfaction of curiosity, another to devise a waveform which will allow power to be transferred without a given power meter indicating accordingly.

That is, there's two ways one can interpret "free power": either violate the laws of thermodynamics, or others...

ISTR some very modern rollercoaster -- using linear motors and very high surge currents -- registered surprisingly little electricity use. Eventually they adapted the meters accordingly.

Thomas Prufer

[Derek Geldard]

Even if the current is not switched on until it's 90 degrees out of phase ?

That's so inaccurate as to be no use whatsoever.

DG