low energy bulbs again - how low energy?

[KeithLT]

Lower A/C costs.

[mick]

Correct, but you are giving it back later in the cycle, which effectively shifts the voltage phase relative to the current phase. The difference in phase angle is theta, and the PF is cos Theta.

The supply

Smoke & mirrors. We are looking at the load of a single CFL. Well, I am, anyway. :-) True, lots of CFLs may well eventually "self correct" by all adding their lousy PFs at the right time. lol!

Sorry, but it has to. The load is either inductive or capacitive so it produces either a leading or lagging PF, which is very significant as a % of the load when the PF is as bad as 0.5.

It results because the

Drawing energy only at the peak of the waveform creates harmonics on the mains waveform, introducing distortion and adversely affecting the PF of the load.

Eventually I suspect that all CFLs will contain some form of PF correction in the form of filtering. As the number of them climbs the power supply authorities will probably insist on it - or start charging everyone by VA rather than W.

[whisky-dave]

This is the same problem computer (& most switched mode) power suplpies tend to have, in fact years ago we (the college) were told we'd have to pay more for our electricity due to this power factor because when you have 1000s of computers on site it does add up.

[whisky-dave]

I've seen some 5W MR16 they recon they're equiv. to 20w halogen. £15

thing that I haven't seen discussed is the health issue as a product of brightness. A friend has tried reading under LED lights and gets eye strain I believe this is due to the limited real brightness. Our eyes adapt in dim lights but don;t work as efficiently and our dept of field (what's in focus), and dim light does cause eye strain. So I'm a bit concerned about using dimmer lights to be green if my eye sight suffers in the long term.

I'd also like to find out for myself just how bright a light is rather than rely on the manufactures weighted & obscure specifications. I'm thinking along the lines of using a digital camera as a light measuring tool.

[Tony Bryer]

If that were so, the bulb would just get hotter and hotter!

[mick]

It doesn't work like that. You can't correct for distortion-induced power factor problems by throwing caps at it. That usually results in worsening the PF and setting up resonances in the system.

There is a good (but technical) paper on this here:

is relevent too: this: (very interesting!)

[tom.harrigan]

green

some

Network user not the BBC"! Really, can't you tell? But wait, it gets funnier...

Using the figures from the article you cite we have: CFL - 6mg total manufacture + 2.4mg from power stations = total 8.4mg GLS - all Hg from power stations = total 10mg

Now for the really funny bit - the emissions from power stations is for 100% coal, but we only use 30% coal in UK, giving revised figures of:

CFL - 6.8mg Hg GLS - 3.0mg of Hg !!!!!!!!!!

But there was no way you were going to spot that because you are a credulous innumerate!

Thanks for the information, now there is no need for me to consider the shocking inefficiencies of Chinese brown coal power plants etc.

T

[mick]

Good point. Another is that manufacturers have no interest at all in using high quantities of mercury as it isn't a cheap metal to extract or manage. I'm pretty certain that they are attempting to keep the amount as low as possible.

[tom.harrigan]

green

some

Network user not the BBC"! Really, can't you tell? But wait, it gets funnier...

Using the figures from the article you cite we have: CFL - 6mg total manufacture + 2.4mg from power stations = total 8.4mg GLS - all Hg from power stations = total 10mg

Now for the really funny bit - the emissions from power stations is for 100% coal, but we only use 30% coal in UK, giving revised figures of:

CFL - 6.8mg Hg GLS - 3.0mg of Hg !!!!!!!!!!

But there was no way you were going to spot that because you are a credulous innumerate!

Thanks for the information, now there is no need for me to consider the shocking inefficiencies of Chinese brown coal power plants etc.

T

[tom.harrigan]

You conveniently attribute all UK power generation to coal. Only 30% is coal. Setting aside the energy and pollution of manufacture, and the actual amount of mercury used in manufacture, even with your optimistic figures, incandescent bulbs still win.

T

[Andrew Gabriel]

It has to be made very pure for fluorescent lights too, or quality goes to pot. I think it's 4 times distilled to get to the required purety.

[tom.harrigan]

So where do they dump all the contaminated gunge left at the end?

T

[Andrew Gabriel]

Yes indeed (although I'd prefer to say you shift the current phase relative to the voltage phase, as you only control the current).

Well, it explains the issue you brought up of why the generator only needs to supply the power used, and not the VA.

OK, it can be different when you only have one load (depending if the supply is one you can feed power back into). A UPS or inverter will not be able to take back the power you didn't use for reuse (and might actually waste further power trying to absob it), and will need to be sized for the VA. An older simpler rotary generator may be able to take it back and store it in the rotor inertia so it doesn't need quite as much fuel to maintain the speed.

It's different loads with different PF's and shifts which benefit from this, although they don't have to be net balanced.

This is wrong. A load which is inductive or capacitive has a phase shift and a resulting PF < 1, but this is not the only way to get a PF < 1.

Exactly -- you have no phase shift, but you have another way to get PF < 1. (Well, you could do a fourier transform of the peak pulse current waveform and work out all the harmonic compontents, and try to argue that all except the fundamental are shifted, but as they're not at the mains frequency, that's inevitable. Given the fundamental is not shifted and the other harmonics will all be odd ones and symmetrical, I would argue there's no phase shift.)

EU has rules for switched mode power supplies (which is what CFLs use). Those above a certain power rating must be power factor corrected, but I think all CFL's fall below this limit. It's quite easy to make them power factor corrected just by removing the smoothing capacitor, but you get 100Hz flicker, and a drop in the efficiency of the gas discharge due to stopping and starting it at this speed. There are more complex ways to correct the PF of a SMPSU, but not very consistant with a cheap throwaway consumable.

[Bob Eager]

Needing more energy...

[Andrew Gabriel]

Boiling 3mg of mercury, hum. Actually, the lamp does that every time you switch it on.

[Mary Fisher]

Leaded petrol WAS banned.

Today's fuel; for cars - even the cars themselves - one day will be banned ifonly by people, because there are better alternatives.

You don't watch tv in the hall though - well, most people don't in my experience. We don't watch it at all.

I wish I undertstood all that ...

Ah, the power of the pocket. Well, if money is important to you I suggest you switch to low power bulbs and efficient gadgets.

Mary

[David Hansen]

On Fri, 11 Jan 2008 13:18:19 -0000 someone who may be "whisky-dave" wrote this:-

Indeed. That is why heat recovery luminaires (in large air- conditioned buildings) involve sucking hot air from the ceiling and making use of it elsewhere. If the hot air was of use at ceiling level the expense of doing this would not be worthwhile.

[Mary Fisher]

...

Ah - 'I heard it on the BBC so it must be true' ... perhaps you're too young to remember that refrain :-)

Mary

[Mary Fisher]

Most things appear so when taken out of context.

As does 'how naive' (sic)

Mary

[Mary Fisher]

>> One thing that I haven't seen discussed is the health issue as a product

As someone else, perhaps not here, the matter of perceived brightness is subjective.

Mary