Dimmer Switches

Something I posted before about a similar test I did:

"Mains voltage was 243V, and measuring RMS current draw (true RMS clamp meter) at the switch I got a reading of 0.40A at full brightness. Reducing to approx half brightness reduced the draw to 0.30A, and at minimum brightness the current draw was 0.17A, so 97W at full, 72W midway, and 41W at minimum. (this was feeding a track light with four fittings - each with a 25W bulb)"

(with caveats regarding how well true RMS clamp meters handle the choppy nature of a dimmers waveform!)

I might go and do another test in a bit - I have some other lights here I could measure...

Clint Sharp wrote on 07/02/2009 :

However the point is that the lamp itself becomes even less efficient at converting electrical energy into light and more heat by proportion is produced. This is true whether a dimmer or simply putting two lamps in series.

While there will be some of that (though not much) the bulb just becomes less efficient. It generates less visible light for the amount of heat it produces.

-- Jason

Two things happen:

1. Because the bulb is dimmer, it is less hot, and so its resistance is lower. That means for the half time that the current is being supplied, more current flows, so it is using more than half the power of full on.
2. Running dimmer means it is running less efficiently. Its spectrum is skewed more towards the red and infra-red end and so gives off much less than half the amount of visible light.

-- Jason

Turn it down a bit more and what do you have? A 200W bathroom heater :-)

Yes, looks like we're all measuring the same effect (sigh of relief :). I'll add a data point for posterity as the kit was already out on the bench ... One year old, 60W pearl bulb, fitted in an Anglepoise, 1mtr above bench and in line with light meter. Local supply 248V~. "Dimmer position" measured using oscilloscope. Bulb maximum power 62.8Watts. Maximum light out was 546 Lux.

% Dimmer setting: % max Watts: % max light

I.e pretty rubbish below 1/2 setting.

Anyways, why do the Philips and Ikea "20W" CFLs give -exactly- the same light as a 60W incandescent, when the packets say they're equivalent to 100W?. Seems an outright lie to me. I think we should be told ;)

Useful set of figures... can I pinch that for the wiki?

because they are comparing to a 100W "soft tone" bulb (i.e. a almost mythical dim one!) ;-)

It is a lie, and we've explained why many times (comparison is against softone filament lamps, which are particularly inefficient as they have a coloured painted bulb).

However, you are also hitting another effect in your anglepoise, that the light distribution isn't the same from a CFL and from a filament lamp. Most CFL's have a noticable drop in light output on-axis, so you'll see particularly low value from an anglepoise.

Generally, there's about a 1:4 power ratio for same light output - use that as a guideline and ignore the equivalence on the packaging. For reflector lamps, this will drop to 1:3, or even 1:2 for the very small ones.

Or put another way, as the temperature of the filament decreases, the mean (or do I mean median) colour of the output passes from visible to infra-red

John Rumm wrote: [...]

My pleasure ;)

F****** weasels. I've spent a lifetime assuming there were laws against scumbags making this kind of specious advertising. Looks like the lobbyists won out. Ah well, I live and learn!.

If you don't like it complain to the ASA! I have done so several times (for various reasons). Hasn't changed anything - I get the distinct impression that single complaints tend to be dismissed but when there are lots it becomes a 'story' and they take more notice, and it is sometimes taken up in the media.

"In Touch" the Radio 4 magazine for the blind and partially sighted had an interesting item about CFLs. Apparently many partially sighted people cannot see by the light of CFLs but can see well enough to manage stairs in the light of an incandescent bulb. They see a ban on incandescent bulbs as discriminatory.

Thanks Andrew. I was sure it would have been done to death and had seen a couple of threads in back posts. Just adding another voice of complaint!. Yes, I know what you're saying wrt the measurement and is the reason the test was done with the lamp in a single socket 9' up in a

Yes, they do, although I'm not sure how much, I checked mine using one of those wireless energy monitors while dimming a set of 6X50W mains halogens.

Checked the Philips carton again, found the dog turd in unreadable

One massive advantage of using a dimmer is that it greatly prolongs the life of the bulb. My main sitting room light uses three 60W 'golfballs' They have never been changed since I bought the house 22 years ago. The light is used every day - though rarely on full power.

I also use golfballs and candles in other parts of the house. They are not dimmed and seem to last less than 3 years. GrahamC

You have paid _vastly_ more in higher electricity prices due to running the lamps inefficiently than you have saved on new bulbs.

Unless they are clear glass, they have a painted coating which is also very inefficient compared with the regular pearl GLS diffusing coating.

Where does the extra sum come from?

MBQ

Good point . The average takes the sum anyway. The text parses better as ..." the square root, of the average of the squares, of t..." Or more concise ... Sqrt( [a1^2 + a2^2 + a3^2 + a4^2...an^2 ] / n )