Dimmer switch or not?

We have a 5-arm centre light fitting which currently has 5 x 60W lamps in it. We sometimes have a requirement for such brightness, ie, when my father-in-law is staying with us, but for the majority of the time we could manage with much less - and perhaps save a bit of cash/carbon as well.
I'm finding it difficult to acquire either 40W or even 20W lamps that look good in this fitting and I don't want to just take lamps out as that looks stupid, so wondered about a dimmer switch. Does a dimmer switch actually cut down the energy used or would the total draw still be 300W with, for instance, the lamps taking 150 and the other 150 being dissipated in the switch - if you see what I mean?
Thanks
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Dave explained on 11/02/2010 :

It will save some, but not as much as you would really expect.
Not much at all is wasted in the dimmer, but as you turn the brightness down, the efficiency of the lamp deteriorates rapidly - you get much less light and a much greater proportion of the energy turns to heat from the lamp.
The old fashioned method of having two switches, one controlling two lamps, the other three - giving you the option of 2 or 3 or 5 lamps lit, was quite efficient.
Could you perhaps use dimable CFL's? I would imagine these are much more efficient even when dimmed.
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Harry (M1BYT) (L)
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May be efficient but looks odd.
--
*Women who seek to be equal to men lack ambition.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Looks better on a 6 arm, IMHO. I've done one (with controller and triacs on-board) that could run 1,2,3,4, or 6 lamps at a time, selecting appropriate combinations for "balance". I've also done with 8 lamps on a spiral strip, simply lighting them in turn from the base of the lamp.
I think there's even an X10 controller for doing this.
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Some of these comments about lamp 'efficiency' and heat, ignore the fact that, if you think about it, ALL electricity coming into a house, with the exception of a) Outside/garden lights b) Clothes dryer exhausting directly outside c) A certain amount of electrically heated hot water that goes straight down the drain, becomes heat within the structure!
Even the light striking the walls, furniture and persons within the building, a few milliseconds after it is emitted becomes heat. In a cool climate that dissipation is part of the heating requirement of a building. Explains why sometimes, in cold weather all the lights in building are blazing; in order to provide some its heating needs! And where AC is needed it can be part of the heat load that the building systems have to get rid of.
So why all the worry about lamps being 'inefficient'. If five bulbs at full brightness is 'too much' then maybe five at only 80% activation (chopped up waveform etc.) will be about 65% the amount of light; and it may be less than that and a different colour, because the lamps themseleves are not as hot. So maybe around 50% effective light?
e.g. 80% = 0.64, 70% = 0.49, 60% = 0.36, 50% = 0.25, 40% = 0.16, 30% = 0.09, 20% = 0.04
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My understanding is that the dimmer 'chops' the AC waveform so in effect switching the light off for part of the 50Hz cycle - so not much is wasted. However as bulbs are really little heaters - halving the brightness doesn't equate to a 50% saving in energy - perhaps only 10%. The incandescent 'range' of a bulbs output is at the top end of its energy usage.
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Dave wrote:

It does save some energy, but the saving is not proportional to the reduction in light. So at 10% light output you may still be using 50% of the power.
What sort of bulbs does it use?
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John.

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Dimming just turns down light and energy goes to heat instead, its pretty but dosen`t really save power.
Thought about perhaps table and floor lamps more specific to room use , allowing centre fitting as cleaners/FIL light?
Cheers Adam
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Adam Aglionby expressed precisely :

It does use less energy. 50% duty cycle will use half of the energy, but very much more of that 50% will proportionally be turned into heat than light. The lamp itself becomes much less efficient at converting energy into light. Lamps work at maximum efficiency when the element is white hot, rather than the red hot when dimmed.
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wrote:

Very true, trying to oversimplify the relationship between power in and light out, at 50% power out ,visibe light out will be considerably less than 50% of full. Phase chopping dosen`t end up in a totally linear realtionship with control position either.
Cheers Adam
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writes

It's difficult to imagine lamps that are available in 60W but not in 40W, go on, tell us what they are.
On relative efficiency and dimming, here's an extract I took from a study a while back:
300W at full brightness costs 300W (100% _relative_ efficiency) Dimmed to half brightness costs 230W (65% rel eff) Dimmed to quarter brightness costs 170W (65% rel eff)
ie. your savings are not great.
The answer is probably to drop to 40W lamps and let your FIL squint a bit when he visits.
My preference now is for table lamps with CFLs that are on for the whole evening. The top light uses incandescents but is rarely on, the light would be too harsh.
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fred
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Bollocks, the last one should read 44% rel eff.
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fred
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We have exactly the same - have been using the halogen "energy efficient" bulbs in an attempt to save a bit. Not convinced...
http://www.toolstation.com/shop/Lighting/Spot+Lamps/Sylvania+Halogen+Ball+Energy+Saver+28w+SES/d220/sd3074/p49436
http://preview.tinyurl.com/yfkpzes
40W and 60W equiv are available - and unlike CFLs the equiv rating is plausible.
The work fine with dimmers, but I'm not convinced they last all that long. The filaments appear to droop over time and then break.
I might be imagining it, the stupid fitting always ate bulbs anyway. YMMV.
Darren
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On Thu, 11 Feb 2010, D.M.Chapman wrote:

http://www.toolstation.com/shop/Lighting/Spot+Lamps/Sylvania+Halogen+Ball+Energy+Saver+28w+SES/d220/sd3074/p49436
I am looking into the R50 equivalents. Do they really make financial sense? I guess it depends on the kWh cost. Do they last twice as long as the standard ones (even if not 2,000h)?
Cheers,
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Reflector lamp CFLs are really poor. LV halogen and some patching of the holes works better.
Cheers Adam
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Halogen downlighters fare badly too. They may have higher lamp efficacy than GLS, but their method of installation means that the overall install is much less efficient, and way more energy is used.
NT
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This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools.
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On Mon, 15 Feb 2010, NT wrote:

Any answers to these still gratefully received.

Thanks, but I would rather not do all that. :-) I am also a bit concerned about high currents and transformers in the heavily loft, but I may be wrong.

Interesting, can you expand? I have been following the ng and don't recall seeing this before.
Thanks,
-- Kostas ---559023410-851401618-1266308695=:25739--
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R50 is probably generating fair amount of heat ;-)
Trafo per lamp and dont warp them up , high current is only on the output .

Think what NT is meaning is covering ceiling is spots is not good way from scratch for general lighting, they are after all, spot lights not flood lights.
CFLs aren`t spots and dont adapt well to spot style housings, heat is the premature end of them.
In your circumstatnces, change the bulbs, 2.29 a lamp, save 12W per point and get a nicer light , dimmer switch will extend lamp life
http://www.gil-lec.co.uk/products/769961011
Cheers Adam

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This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools.
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On Wed, 17 Feb 2010, Adam Aglionby wrote:

(What I should have said above is "heavily *insulated* loft"; apologies)
Sorry, what does "warp up" mean? I am interested in this, as in another room I have GU10s that may be changed to LVs without plastering needed (I think).

Ah, yes, I have followed this, thanks. I thought NT was comparing halogen downlighters vs standard downlighters.

Interesting statement about the nicer light. One of the aspects that concerns me is the beam angle. I found some 40W Halogens R50s (GE) cheap the other day and tried them, but found the beam too concentrated.
Yep, I already have dimmers, I hope we are still On Topic. :-)
Cheers!
-- Kostas ---559023410-959030623-1266657490=:26846--
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Sorry my bad typing, meant wrap
Electronic trafos are thermally protected , if they overheat they shut down, classic symptom of `flashing ` lv downlights, overheating trafos.
They dont get incredibly hot but need some free air around them, tafo per lamp is usually easier.
LV fittings also need an air gap behind them because the heat goes backwards, the dichroic bit. GU10 are aluminised and heta goes forward, get GZ10 mains voltage dichros but almuinised LV are beside the hens teeth :-(

Darn, side effect of smaller filament in lamp,its something that may vary a bit by brand, some ludicrous prices being quoted for halogen R series, some of the `eco ` vendors sticking it right in at 5 odd quid a lamp.

Well brought back round :-)
Cheers Adam

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