How come Energy Saving lightbulbs seem to use a lot more watts than their rated level?

Question

I bought an efergy smart meter to monitor my power usage. It reliably reports 300W usage when I turn on 300Wats worth of halogen bulbs (well 310W actually) or 2KW when I turn on my 2KW kettle. When I turned on an old 15W CFL bulb its said 52 Watts, then went up to 69 watts, then back to 52, did this a few times then settled at 52 W. I thought its probably old and goosed so I bought a couple of new 20W CFL's, they both came on at 34W, then up to 52 for a while then back to a steady 34W, better but still well over the advertised 20W Rating. The bulbs are A rated for energy efficiency.

I suppose the hop up on starting will be the normal fluorescent starting current, its the long term higher wattage that worries me.

I did try several of the other CFL's in my house and they all behaved the similarly and drew way more than their rated wattage.

Answer 1

Are you reading the light? The power? Strange

Answer 2

I suspect problems with your meter. Measuring AC power is not so simple, especially with devices that have active components (transistors and transformers and so on), which CFLs have but halogen bulbs do not have. There are questions of reflected power and power factor and things like that which have to be accounted for. I am especially concerned how the reading went up and down before settling at some value. Have you measured anything other than lights? A computer? TV? Something with a motor or transformer? How well did it do?

Answer 3

It is possible that the ratings on the CFL package refer to the bulb wattage, not the bulb and the attached ballast.  Unlike regular incandescents, fluorescent lamps need a ballast which draws a small amount of current.

This ballast factor might account for a 15 watt CFL drawing a few watts more than rated, but they shouldn't draw twice the wattage of the bulb.

What is the accurating rating of your energy smart meter?    It's possible that your meter reads well at higher wattages (such as 300W or 2000W) but not as accurately at low wattages (15W).

Those are the only two reasons that I can think of for the discrepancy.

Good luck.

Answer 4

you have got me thinking, thanks for that i will try mine out.

Answer 5

They should settle down to their rated level once they are fully warmed up.  But you're right, in a normal usage cycle they do tend to use about double their rated power.   Fluorescent light bulbs are energy intensive to make and a major disposal hazard.  You're not supposed to put them in the bin - but that's what most people will do.  They are being forced upon us on an invalid argument.  I can only assume that someone is getting a huge bung.

The future is likely to be LED lampbulbs.  These should use considerably less power than even the rated wattage of fluorescent bulbs, they will last for decades and not represent a major pollution hazard.  Unfortunately, they are still about 5 years off.  So stock up with tungsten bulbs and save the planet.

Answer 6

Have we all forgotten that these energy saving bulbs have a starter, that uses power initially, do not turn them on and off, never use them in a cupboard, shed or maybe a toilet, they are not energy efficient for short term use!

Answer 7

Temperature and the condition of the wire in the home makes a lot of difference.  

Cool means more power has to be used.  Old wires resist and use power.  

People never think abut this one.  A house thirty years old Will still have the same wiring as when new and most of it will have a very increased resistance because of electrolysis.

Answer 8

Haha I never thought it like that wierd ha...People are so wierd these days dnt ya think?