Is a dimmer and incandescent light efficient?

[405 TD Estate]

Just wondered if the dimmer + light stilll consume 60w when the light is dimmed?

[Styx]

My understanding is that the power consumption is reduced a bit, but nowhere near as much as the light output is. i.e. 50% light output reduction does not mean you are only using 50% of the power -- far from it, iirc.

Styx

[1501]

You should always remember an incandesant light produces light purely as a by-product. They are really designed to produce heat - lots of it

- enough to make the filament glow white hot at design voltage.

[David Hansen]

On Thu, 6 Mar 2008 00:52:51 -0800 (PST) someone who may be 405 TD Estate wrote this:-

At a guess when dimmed to say 50% of the light output the lamp will still consume something like 55W.

[The Natural Philosopher]

Bad guess then.

Humans eyes are logarithmic..'half as bright' may mean something like

1/4 the light power or less.

Anyone who has used a manual camera knows that going from bright sunshine to a cloud passing over is already 1/4 of the light..going down to internal light levels may be HUGELY less..and teh point at which you can't really see color, is absolutely amazingly low.

Whilst its true to say that light bulbs get less efficient at lower outputs, the fact of the matter is that you can see alarmingly well at very reduced light outputs, and a dimmer is a crude, but efficient way to reduce input power.

I would guess, from a more educated perspective, that it's less than 15W at 'half brightness', possibly a LOT less.

But then we know *you* 'don't count', and all of your judgments are predicated on woolly minded emotive bases, and never on facts - especially backed up with informed mathematical analysis.

I can imagine you as a WWI commander: 'keep together chaps when you go over the top. Mutual protection and all that' and the opposition's machined gunners chuckling as they see a tight knot of 'chaps' just waiting to be scythed down in a single burst..

[The Natural Philosopher]

50% less light output barely registers as any different.

You would need to be down about 90% to feel that 'half brightness' had been achieved.

[David Hansen]

On Thu, 06 Mar 2008 13:14:58 +0000 someone who may be The Natural Philosopher wrote this:-

Nice try, but you failed to make a convincing case. You may have the last word.

[The Natural Philosopher]

Sorry, this isn't open to debate. Or debating points scoring. It's open to either sticking a meter on it, or understanding how dimmers, electricity and lightbulbs and the eye actually work.

If you want to stay in your fantasy land of subjective judgments and opinions, fine, but please don't expect anyone to take you seriously.

I spent enough my life with my eyes glued to oscilloscopes, test equipment and god know what understanding the theoretical and practical aspects of semiconductor design, let alone many years as an amateur photographer with a hand held light meter, to have ANY patience with someone as ill informed and unscientific and as totally unversed in practical real world engineering as you are, when it comes to an opinion on something technical.

Nothing I say will convince you anyway. ~I could spend a day rigging up a watt meter, and demonstrate it to you and it wouldn't budge you an inch.

Unlike you, I am less concerned with winning arguments, than with achieving practical results that have meaning, and practical results that are predictable in both performance and cost. Thats what being an engineer is all about.

[Martin Bonner]

[snip]

Hmm. There are two (very) non-linear effects here:

- a small change in input electrical power causes a large change in output light power.

- a large change in output light power is required to cause a small change in perceived brightness.

... and finally, the efficiency needs to include the power consumed in the dimmer (I know it isn't just a variable resistor, but even so there has to be *some* power loss).

But that's 15W in the lamp.

[The Natural Philosopher]

cubic or 4th power I think roughly, buy not exponential whereas..

that is inverse exponential - i.e. logarithmic.

So I would aver that power goes down faster than 'perceived brightness'

It certainly doesn't go down SLOWER as 'dynamo Hansen' reckons..

About a 2v drop when on, no power lost when off. Some switching losses

So about 95%-98% efficient more or less.

[Andrew Gabriel]

Nearly.

One that I measured... A 500W light dimmed to same output as a 40W light was consuming 300W.

[RobertL]

Don't forget that running the lamp at lower power also alters the colour balance (spectrum) of the light it emits. It not just a qestion of the intensity.

Robert

[The Natural Philosopher]

Indeed. apples and oranges.

Warm orange glow as opposed to blazing white halogen.

I would say that my experience of dimming halogens and ordinary lamps shows that the halogens lose light more rapidly than the standard bulbs..

[Adam Aglionby]

Adam

[The Natural Philosopher]

halogens run at half power appear a lot less bright than say incandescents run at half power, when they look similar at full power.

I think its because the halogens are more efficient at full power due to higher temps in the bulb..the incandescnets start from a lower level, and fall away less.

[Adam Aglionby]

Think its possibly because halogen will start at a higher colour temp than a standard incan so transistion to yellow is more marked.

Heres a couple of interesting references:

[David Hansen]

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

It will be interesting to see if the usual suspects attack your posting. Clearly your measurements must be wrong, as they do not tie up with the usual suspects' assertions.

Looking at the times of your and their postings, if propagation is reasonable they have had plenty of time to attack your posting, but they have not done so yet.

[Huge]

I though dimming halogens was A Bad Idea?

[Adam Aglionby]

Your thinking of what is largely a theoretical problem, where the internal tempertaure drops below that high enough to support the halogen cycle, where the halogen, iodine or bromine, catches tungsten molecules and redeposits them back on the filament.

Theory being that at low levels envelope temp isnt high enough to stop the tungsten being deposited on the inside of the enevlope rather than the filament , leading to lamp blackening.

Running lamps at full for few minutes is enough to counteract it, some debate about wether its a real problem though.

Adam

[Martin Bonner]

Hey, no fair! How can we have a good theoretical discussion if you confuse the issue with actual experimental results. :-)

(One question: Was you measurement actually watts, or was it volt- amps? If the power factor is significantly different between dimmed and undimmed lights, then that would invalidate your results.)