Dimmer switch or not?

[Dave]

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

[Harry Bloomfield]

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.

[John]

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.

[John Rumm]

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?

[Adam Aglionby]

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

[Harry Bloomfield]

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.

[Adam Aglionby]

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

[fred]

In article , Dave 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.

[D.M.Chapman]

We have exactly the same - have been using the halogen "energy efficient" bulbs in an attempt to save a bit. Not convinced...

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

[fred]

In article , fred writes

Bollocks, the last one should read 44% rel eff.

[NT]

Dimmers can save a little, but not much. I'd regard their effect as almost purely aesthetic.

There are other ways to reduce power consumption.

CFL is a lousy choice for a chandelier, but looks fine in some fitting styles.

One could substitute 40w lamps and add a booster that switches them between 40w and the light output of 60w while only consuming - I forget the figure but something like 45w. The downside is that in boost mode bulb life drops to about 300hrs. Its still more efficient energy and money wise, but most people dont regard it as worth doing.

Another option is to dismember a set of light bulbs and fit halogen capsule bulb sockets inside them. Fit 12v capsule lamps and run the fitting off a 12v halogen supply. Halogen capsules are an advantage with chandliers as they're a smaller light source, so give crisper and more intense colour splitting. They also cause much worse glare, so downrate the power output at the same time, eg from 60w to 20w.

If light output is reduced, make up the deficit with more efficient and more discreet background lighting.

NT

[Dave Plowman (News)]

May be efficient but looks odd.

[Andy Dingley]

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.

[terry]

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% =3D 0.64, 70% =3D 0.49, 60% =3D 0.36, 50% =3D 0.25, 40% =3D 0.16, =

30% =3D 0.09, 20% =3D 0.04

[James Salisbury]

Dear NT

You can now purchase 230V bulbs that have a halogen capsules in a tungsten bulb glass envelope. So same size as before with the benefits of halogen.

[Andy Dingley]

Anyone seen them in SBC bases yet? I'd go for some of that.

[NT]

and a poor choice. Stick with LV.

NT

[Appin]

The message

from Andy Dingley contains these words:

Yes -- you can get "build your own" components -- bases of different sizes and glass envelopes of different shapes.

[Adam Aglionby]

Got to say those are genius, thanks!

original brochure

tends to bit warmer 2900K rather than 3200K of LV halogen but a better substitute in something like candles and way better tahn CFL in lot of applications.

Up to 100W Halogena and Halolux are GLS halogen alternatives, 150W halogena seems to have dissapeared.

Cheers Adam

[Kostas Kavoussanakis]

> > 40W and 60W equiv are available - and unlike CFLs the equiv rating is > plausible.

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,