# Forum Home Renovation Lighting  Fluorescent light power usage

## pig75

I have a 1200mm fluorescent light in the kitchen and it seems to use to much power. It has a osram 40w bulb and uses 80w of power is this normal? 
As this light is on most of the time i would like not to be wasting 40w in power any ideas would be appreciated

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## SilentButDeadly

The globe is not the only power consuming thing on the lamp...there's the ballast and starter as well.  So the extra 40w is possible but exactly why...I have no idea.  In the general scheme of things though...worrying about 40 watts in a light is a waste.   
Your fridge is just as likely to 'waste' ten times that much if it is not being used or maintained correctly, for example.

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## chrisp

> I have a 1200mm fluorescent light in the kitchen and it seems to use to much power.

  How do you know it is using too much power?   
Be careful of some 'power' meters as some basic ones only measure the current (and maybe the voltage) and don't do a proper calculation for power.  The power factor on some fluorescent fittings can be quite bad making the 'apparent power' high.

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## pig75

Ok i have a 40w circular fluro in the lounge room it uses 55w. I would have thought that they would not be more efficient than a straight tube

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## chrisp

> Ok i have a 40w circular fluro in the lounge room it uses 55w.

  I'm a little confused as to _how_ you are determining the power usage?

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## pig75

I have a power usage meter with every thing turned off we use 0w if i turn the kitchen light we use 80w the lounge uses 55w the side room has a CFL that uses 9w
I would have thought that a standard fluro would be more efficient than 50%

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## chrisp

> I have a power usage meter

  I suppose that what I'm trying to work out is how you are metering the power.  Do you have a brand and model for the meter? 
With AC power, some power meters don't do the VxI multiplication correctly and give 'apparent power' rather then 'real power' (or 'true power'). 
There are many 'power meters' that are actually just ammeters (that assume a particular voltage and an unity power factor) and usually give high reading for power - particularly for inductive loads such as an non-electronic fluorescent fitting..

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## pig75

Its a elite 3.0r meter not that that matters 
If a light is using 80w with a 40w bulb thats only 50% efficient and i might as well have 8 CFL lights as it will use the same amount of power

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## chrisp

> Its a elite 3.0r meter not that that matters

  Actually, it _does_ matter! 
From what I can work out, the product you are using is just measuring the current - and scaling it by a factor to read power. 
Your CFL are electronic and probably have a respectable power-factor so the meter reads about right. 
However, your standard florescent tubes are probably in a old-type 'ballast' fitting (do they have a 'starter' or do they flick when starting?).  The power-factor on these types of fittings is quite poor. 
Your 'power' meter is really just an ammeter and not a true indicator of power.

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## justonething

Some of these fluros have a power factor of about 0.55, I did measure it awhile back. 
A related question if I may, Do electrical meters, especially smart meters in victoria record apparent power or real power usage?

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## LinesElectrical

> I have a 1200mm fluorescent light in the kitchen and it seems to use to much power. It has a osram 40w bulb and uses 80w of power is this normal? 
> As this light is on most of the time i would like not to be wasting 40w in power any ideas would be appreciated

   What Chrisp has said is correct. 
If you still don't believe him turn off everything write down the numbers on your service meter and the time turn on the light wait one hour and then write down the new number. 
This is the only power measurement that matters because this is the one they will use to work out your bill.

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## LinesElectrical

> Some of these fluros have a power factor of about 0.55, I did measure it awhile back. 
> A related question if I may, Do electrical meters, especially smart meters in victoria record apparent power or real power usage?

   I was always told they read true power thats why factory's get penaltys for running lots of motors and fluoros that run down the power factor as it is waisted energy that they generate but doesn't do any work and they can't charge for it.

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## chrisp

> A related question if I may, Do electrical meters, especially smart meters in victoria record apparent power or real power usage?

  The electrical meters (smart and otherwise) measure true or real power and (mathematically) time-integrate to produce energy (the product of power and time).  You are billed for energy (usually in the units of kWh). 
Items with poor (low) power factor result in more current flowing to deliver the same power (compared to a high power-factor item).  You are not billed for this extra current, but the infrastructure (cables, transformers, generators) has to rated to cope with the extra current.  This extra current also causes extra "IR" (current x resistance) losses in the power lines - degrading the efficiency of the power system.  (The system actually has "VAR generators" to help compensate and improve the efficiency) 
In a commercial installation (depending upon the tariff), their tariff might be something like: 1/3 "real power" + 1/3 "apparent power" + 1/3 "monthly peak power".  This is intended to encourage the use of high-power-factor equipment (such as florescent fittings with a power-factor correction capacitor - which are usually deleted to save cost in domestic fittings).

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## pig75

Yes they are old style fluros and like i said the 40w circular fluro in the lounge room it uses 55w witch is much better than the straight one that is using 80w
I always thought that fluros are much more efficient than standard incandescent bulbs 
Power used is power used if i am wasting 40w in heat on each of the old fluros i have down the shed i think i should be looking for more efficient lighting 
Does any body know of a efficient light to replace the fluro might have to find a circular fluro like in the lounge room

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## chrisp

> Yes they are old style fluros and like i said the 40w circular fluro in the lounge room it uses 55w witch is much better than the straight one that is using 80w

  You need to back up here -- The instrument that you are using isn't measuring power.   Therefore, you can't use it to meaningfully compare the power usage of the different lights.   
For example, using the power-factor provided by justonething of 0.55, your 80W "apparent power" using fitting may actually be using 0.55 x 80W = 44W "real power".

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## pig75

Ok so what you are saying is that a 80w standard bulb will use more power over say 10 hrs than this fluro that uses 80w ??

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## LinesElectrical

Might be time to give up Chrisp just like I will never understand how my wife spends all day with a two year old without going insane pig75 may never understand that the reading he is getting of his toy energy monitor is not the same as what he is actually using. 
Besides he answered his own question he should replace his old lights they are waisting energy he just is not paying for the extra waste directly.

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## chrisp

> Ok so what you are saying is that a 80w standard bulb will use more power over say 10 hrs than this fluro that uses 80w (apparent power) ??

  Correct. 
The correction factor between "real power" and "apparent power" is called the "power factor" and it is a parameter of the equipment using the energy (i.e. the power factor is a characteristic of the light fitting itself). 
You can work it out for your individual lights if you're keen - turn everything off except the light in question.  Read the power on both your electricity meter (I'm assuming that it is an electronic one that give a power figure) and read the "power" on the other meter.  The power factor is the reading on the power company meter / reading on the 'other meter'. 
LMK if your meters read energy (such as kWh) instead and I'll give you an alternative method.

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## pig75

This is my meter. It would be great if you could tell me how to work this out

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## chrisp

> This is my meter. It would be great if you could tell me how to work this out

  Basically, you'll need to read the total kWh figures from both meters; leave only the one light on for a period of time; reread the meters again; and work out the ratio of the two readings (=power factor,  which is less than 1).  The problem is that the meter reads in kWh but the light is 40W which is only 0.04kW.  Therefore, if the light was on for one hour, the mains meter will only change by 0.04 kWh (2 hours == 0.08 kWh, etc.).  If the meter is not that accurate - or rather if doesn't display the reading to that resolution, you might need to leave the light (only) on for, say, 10 hours so that it uses 0.4kWh. 
Your power meter is similar to the meter on my place.  I'd need to check the actual resolution on my meter so I can give you a more meaningful response on how to work out the power factor.  However, I'm not going to be able to do so for a few days, or maybe a week or so.  *In the meantime, perhaps some other forum members may like to jump in here and help???*

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## justonething

What I can add is that power factor and energy efficiency are two completely separate and independent concepts (neglecting peripheral loss). Power factor is explained in wikipedia Power factor - Wikipedia, the free encyclopedia. Even though a PVA meter measures 80W, the fluro is only actually using energy at the rate of say 50W. The reason for that is explained in wikipedia. Whether the light fitting is efficient or not is quite a different matter.

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## Johning

Firstly, nothing to do with power factor, but may be of some interest.
 I wanted to find out how much power was being wasted in the ballast of a linear fluorescent light fitting so I conducted this experiment about 4 years ago. I still have the rotating disc type of electric energy meter monitoring the electrical energy consumption of my house which was used to measure power consumption.  
 The tube was a Philips TLD 18 W.
 Results were that with the main switch off: the meter was showing 2 W (measured by counting disc revolutions over a set time). I assumed that this was the power consumption of the meter itself. With the main and light switched on the meter showed a power consumption of 30 W.
 Final result:
 Meter consumed 2 W
 Fluorescent tube 18 W (if you can trust what is written on the tube)
 Ballast 10 W  
 Secondly, CFL and power factor.
 If you look at the side of a CFL it will show the rated current.
 Example: Philips 20 W CFL shows 150 mA. i.e. 34.5 VA or PF of .58
 Example: Osram 8 W CFL shows 80 mA. i.e. 18.4 VA or PF of .44  
 If I have done my sums right CFLs also have a pretty bad power-factor.

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## Smurf

> Ok so what you are saying is that a 80w standard bulb will use more power over say 10 hrs than this fluro that uses 80w ??

   But the fluoro isn't actually using 80W. 
You are measuring current and the fluoro is using about 0.33 Amps. But current is not what your power company's electricity meter is recording, and is not how the power company bills you. 
The power company will bill you for true power only, not current. And the true power of your 40W fluoro is not going to be anywhere near 80W. Realistically, it will be about 50W each for both the straight tubes and the circular. 
Apart from the physical shape of the tube itself, the electrical components are the same for both types of light. You have a ballast, starter and the tube. All up, they use about 50W of true power, but the ballast draws additional current (which your electricity company does not charge you for) which will fool a current-based meter into thinking that the load is higher than it really is. But thankfully, the power company's meter is able to record this correctly and you will only be charged for 50W, not 80W. 
The difference in measurement is due to "power factor" which is a technical term. In short, having a low power factor means the appliance (in this case the fluoro) is drawing more current than true power.  
But since the power company does not charge you for this current, they measure and charge you for true power, there is no reason for an ordinary householder to be concerned about this. It is of interest only to electricians who need to calculate the current in order to know what size wire to use, and to engineers who need to know for essentially the same reasons. In a domestic installation, it has zero relevance to how much the power company will charge for your electricity supply, or to how much it costs to run the fluoro light. 
The 40W circular and the 40W straight fluoro tubes would both cost almost exactly the same amount to run as measured by the power company's meter. Their actual true power will be about 50W in both cases, meaning that they will take approximately 20 hours to use one kilowatt hour (or "unit") of electricity as charged by the power company. 
Your power company will be able to tell you how much they charge for each kilowatt hour consumed. 
Somewhat off topic but the power industry does in fact have the means of "recovering" this excess current drawn by low power factor appliances. There are two means, one using huge capacitor banks (usually located at electricity sub-stations) and the other by using the power generators themselves as a synchronous condenser. It's a complex subject but suffice to say the energy itself is recovered, such that there is not coal etc being wasted, but that this excess current does have to be carried through the power lines.  
Avoiding having to carry that extra current through the lines, which means that the lines need to be bigger than they otherwise would need to be, is why there are restrictions and/or financial penalties placed on large commercial users to encourage them to not use electricity in this manner.  
But the power industry doesn't impose such requirements on ordinary households for two reasons. Firstly, because the average household doesn't have many such appliances such that the actual amount of extra current being carried through the lines isn't enough to worry about and secondly because it's just too much hassle to worry about this sort of thing for the average household. It's more practical that the power companies take care of it at their end.  
In short, the cost of running the fluoro's is based on a load of 50W. :Smilie:

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## pig75

This really has me confused  :Confuzzled:  
Am i right in thinking that the fluro is bouncing some power back and my power monitor is adding this to the total ? Or am i totally off track

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## chrisp

> This really has me confused  
> Am i right in thinking that the fluro is bouncing some power back and my power monitor is adding this to the total ? Or am i totally off track

  Actually, you are right on track and are not confused at all. 
Electrical appliances such as fluorescent fittings are "reactive" loads.  They actually draw and return (some of the) power during different parts of the 50 Hz cycle.  So you are quite correct, there is some power "bouncing back" - I like that terminology.  :Smilie:  
The so called power monitor you are using is just a current meter (ammeter).  It can't determine the direction of the power flow and produces an erroneous "power" reading.

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## pig75

Thanks for the reply  :Smilie: 
Is there a cost effective way of measuring these devices power usage accurately ?

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## Bloss

Not sure why the demand for accuracy when looking at energy efficiency and saving power in the household. Even if an 80W lamp is using 100W (which it won't be) that's not really the issue - much better devices are. 
The easiest and free is to simply use the nominal rated power of the devices or lights or whatever then look at alternatives to replace them which have significantly lower rated use for a roughly equivalent performance. So for example it is still cost effective to replace 40W fluoros with 36W or go further to T5 28W (which I think do not work all that well and need a new fitting too!) or LED replacements (of decent quality). At the moment the early adopters will take longer to get money back, but given the long life of good LEDs for example if you can afford it and be staying put they could be OK. 
If you have downlights then get rid of them all - at 50W they are diabolical at 28W 'energy saving' halogen still bad. Use decent LEDs - replace with MR16s or better still go GU10s at 240v and get rid of transformer. Buy single 'off' units so you can turn banks of appliances with one switch and so on. So for example I have 9W LEDs in a number of my downlights (I replaced many altogether as they are not a very useful lighting design anyway) and get great lighting. Not the el cheapo's and not the most expensive, but good enough. 
Of course if you still have poor thermal management of your house then the electrical item use will be a small part of your over all energy use. Likewise if you have not an efficient HWS then worrying about the lighting and household appliances is a bit misplaced. If you use an air-conditioner then keep the temperature degrees set 2 degrees  higher in summer, and if you have a heater in winter run it 2 degrees lower. Both will mostly save more than anything you will do with lights or appliances - as will not using them and simply wearing appropriate clothes . . .  Of course if you use outside shading and a range of other passive thermal controls then they too will be far more effective than appliances. 
I have no idea what your house is like of course - if you have done all these things and lights and appliances are the last thing then just my 1st suggestions - you can do it all too (I have). But small actions make small savings - big actions make big savings and doing it in the most effective to least is the most cost efficient and effective way.

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## Smurf

So far as energy efficiency is concerned then if you are somewhere cold (Vic / Tas) then heating is by far the biggest energy use in the average home so start with that. 
In warmer climates the big users tend to be hot water and in some cases air conditioning. 
Lighting and general appliances are always last on the list to worry about - focus on the heating, hot water and (if appropriate) cooling first. Even if you left either of the 40W fluoros running 24/7/365 it's still only going to use a tenth as much energy as you're likely to be using for hot water.

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