Actual Watts Used By CFL Bulbs?

C

CF01

Active member
I ordered some bulbs for photo/video lighting that are rated as 45 Watt (200 incandescent equivalent) 2800 Lumens. The light they were giving off looked really weak for those specs, so I plugged them into my Kill A Watt P3 to measure the actual watts being used and I was only getting a reading of about 27 watts each. Every other CFL I've ever measured has been what it was listed as. I found some comments from another user of this particular bulb that reported nearly the same thing as I found. Is there some way that a bulb can be labeled as I described and still be "correct" with the measurement I got? These are from one of the popular super cheap video/photo lighting companies. I wont name the company in case this is just a misunderstanding on my part, but it looks like some kind of really bad quality control or, worse case, outright fraud.
 
CF01 said:
d. Is there some way that a bulb can be labeled as I described and still be "correct" with the measurement I got? .
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The short answer is no, if you measured 27 watts with a reliable meter it is 27 watts. Anything else is voodoo marketing or mislabeling.
 
CF01 said:
I ordered some bulbs for photo/video lighting that are rated as 45 Watt (200 incandescent equivalent) 2800 Lumens. The light they were giving off looked really weak for those specs, so I plugged them into my Kill A Watt P3 to measure the actual watts being used and I was only getting a reading of about 27 watts each. Every other CFL I've ever measured has been what it was listed as. I found some comments from another user of this particular bulb that reported nearly the same thing as I found. Is there some way that a bulb can be labeled as I described and still be "correct" with the measurement I got? These are from one of the popular super cheap video/photo lighting companies. I wont name the company in case this is just a misunderstanding on my part, but it looks like some kind of really bad quality control or, worse case, outright fraud.
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You need to measure the bulb output in lumens, well, actually lux/footcandles, at distances, using it howeer you have it setup... to get an accurate measure of what you 'want to use'... using 'watts' really only works if one knows the efficiency, or the 'lumens per watt' value. I bought some non-photo CFL's recently, I didn't bother with the 'watts' or 'equivalent watts', but rather for the lumen output that the manufacturer indicated on the box... which was 3700 lumens, and 5000K... I'll see if the output remotely reaches those specs...

But for me, if a bulb is rated for 45 W... and is only drawing 27... there's something wrong...

As a side note, just stating the 'lumens' is difficult to get to 'how many footcandles are incident on the scene, given a light in a reflector... etc... Lumens are in terms of a 'sphere' around the bulb, and obviously, for photo work, some form of 'focusing' needs to occur for most applications... this leads to using steradians for the 'cone' of light that is formed with a bulb and reflector... ending up it's just easier to measure directly...
 
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Good on measuring the light output.

I hope Guy Holt checks in here because I think the built in ballasts on some CFLs are not power factor corrected and in that case I wonder if the wattmeter can be accurate?
 
Different manufacturers with seemingly the same product have different specs and performance ratings. If the unit measured 27 watts, then it is what it is. If all their inventory of the same product is within a tight margin of + or - 10% of that rating, well then it is obviously a 27 watter and either their measurements were not done with the same instruments and/or procedures as you have. Rating a bulb as 45 watts and in essence is drawing 27 in reality is a good thing provided that the lumen output is as a 45 watt equivalent. Highly doubtful. If your 27 watt bulb is indeed shelling out 2800 Lumens, then you have a really efficient one that approaches holy grail of LED efficiency territory of the over 100 lumen per watt. If you really want to find out, you really have to actually measure thebulb's output in lumen value. Don't be surprised that 27 watts may amount to a value far less that the 2800 lumens as rated. Also to consider and ask, at what distance from the bulb ( light source) are their measurements taken ?? Hmmm, perhaps half the distance of the norm to have those lucrative figures.
 
perhaps it is voodoo marketing, meaning they are saying the wattage number as if it were the wattage of a tungsten bulb with equivalent output. My guess, and it's very lame, yes.
 
I guess I don't know whether the Kill A Watt is accurate when current and voltage are out of phase which results from the CFL ballasts having power factors typically around 0.5.

I'd love to see the lumen output of the lamps, which, as has been pointed out, is all you really care about and power consumption is just a proxy for it.
 
Thanks for all the comments. I'll just return these to the online store I purchased them from and try a different brand.
 
Chris Santucci said:
Also, keep in mind the CFL units put out less light when upside down from what I understand.
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I did a quick search, from the 'glossy brochure style FAQs'... unless a bulb is specifically marked as requiring an orientation... they should operate in any orientation...

Of course the glossy brochure didn't mention if there was any output differences between orientations...

This means yet another 'spec' to look for... or yet another opportunity for Home Depot personnel to look at me like I'm an idiot... 'they work just like regular lightbulbs'...
 
But note that many incandescent "regular lightbulbs" are specified to use (or avoid) certain orientations. Many bulbs for stage/portable use specify "base-down" etc.
The main prohibitions I remember concerning CFLs, are those dealing with using them in enclosed, insulated, ceiling downlights where the heat builds up in the can right around the PC board where the CFL electronic components are located. Of course, heat is generally bad for all electronic components.
 
"Recording audio without monitoring is exactly like framing and focusing without looking at the viewfinder."

True, but I've heard this more than once: "Dang, I forgot the headphones, but not to worry, I know what good sound looks like." :)
 
They work in any orientation, yes. But when inverted, the ballast electronics are subjected to heat from the tube and even though some (household, I'd imagine) CFLs are rated when inverted, I'd stay away from that practice regardless.
 
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