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I have two (supposedly CFL) E27 light bulbs with similar but different labels:

  • 13W 665lm 8.000H 2700K 230V~50/60Hz 110mA
  • 15W 10.000H 805lm 230V~50/60Hz 118mA

Given that 230V is effective voltage, my power calculations do not match the ones on the labels.

  • P = U * I = 230V * 110mA = 25,3W != 13W
  • P = U * I = 230V * 118mA = 27,14W != 15W

I am aware that power may be less if reactive resistance is not negligible, but I still do not understand how to read the label. What do voltage and current values really mean? Can somebody point out an authoritative source for me?

Update: both lamps have been bought in Sweden so EU rules apply, although the first one seems to be imported from Norway.

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  • \$\begingroup\$ Are those . or , in the H numbers? Is is 8 Henries, or 8 thousand hours? \$\endgroup\$
    – Majenko
    Jan 4, 2015 at 11:13
  • \$\begingroup\$ I believe it's 8000 hours. \$\endgroup\$
    – mkalkov
    Jan 4, 2015 at 12:02

2 Answers 2

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This is kind of a complicated subject, and the composite number "Power factor" is not the best way to describe the distorted waveform that small self-ballasted CFLs and LED lamps draw.

In any case, you can consider these lamps have a "power factor" of around 0.5. There does not appear to be any requirement to mark or disclose the actual numbers (such as THD and displacement factor, or PF) in the EU, only to conform to the regulations.


As a consumer, the important thing to know is that the stated watts is the nominal energy consumption (what you pay for when the light is on), the current is a number that's mostly important for fusing and wiring requirements (if you have 85 lamps at 110mA each, you'll need a 10A circuit at least, maybe more if other regulations come into play). You only pay for power consumption, the power factor (or displacement factor and THD) is a concern of the power utility (and the EU bureaucrats they lobby to regulate it so you'll pay a bit more for the kind of lamp they would like to see connected to their power grid).


Of course the other markings are nominal life in hours, light output in lumens, nominal power input (volts/Hz) and color temperature in Kelvins.

Here (LightingEurope EU Compliant Requirements Products Sheets for LAMPS 1st Edition 29th November 2013) is a comprehensive roundup of the applicable regulations and what has to be marked and what has to be disclosed:

Here (Impact of Energy Saving Lamps on the Power Quality of the Grid) is a fairly technical, but quite readable, document on the matter.

Here (IEC 60969 - Self-ballasted compact fluorescent lamps for general lighting services - performance requirements) is a draft IEC document that goes into the matter in some detail.

The final IEC documents are not free, however you may be able to access them in a public library if you have a burning desire to do so.

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    \$\begingroup\$ Note that the TLDR section is normally expected to be shorter that the section it is meant to replace :-). \$\endgroup\$
    – Dave Tweed
    Jan 4, 2015 at 13:24
  • \$\begingroup\$ I was about to post a similar answer after reading this article. However I couldn't find regulation links on my own. I'll check them out as soon as I get home. What does THD stand for? \$\endgroup\$
    – mkalkov
    Jan 4, 2015 at 13:27
  • \$\begingroup\$ @DaveTweed A very astute observation- modified. \$\endgroup\$ Jan 4, 2015 at 13:52
  • \$\begingroup\$ @mkalkov Total Harmonic Distortion \$\endgroup\$ Jan 4, 2015 at 13:53
  • \$\begingroup\$ I finally got time to go through the links. Thank you very much for them! By the way, as per the second link (slide 11) typical displacement of "electronic lightning equipment" is above 0.9, which means with PF of 0.5, THD of my lamps has to be around sqrt(3). \$\endgroup\$
    – mkalkov
    Jan 9, 2015 at 19:29
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In my experience, the power rating for a light bulb (e.g., 13W, 15W) is intended to be a "nominal" or "typical" value to be used for comparisons with similar products in terms of light output.

On the other hand, the current rating (e.g., 110 mA, 118 mA) is a "worst case" measurement, to be used for evaluating its compatibility with fixtures, and for estimating the overall current required for a multiple-bulb circuit.

Also, the current rating accounts for the non-unity power factor that such bulbs exhibit.

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