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This is the box of a LED spot I just bought. I'm wondering why the power consumption is measured in kWh/1000h and not simply in Watts.

Photograph of box

Edit:

The labeling standard can be found here. (Guide for the application of the commision regulation (EU) No. 874/2012 with regard to energy labelling of electrical lamps and luminaries).

stefandz
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Lior Kogan
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    Because they think you're a dumb consumer. – Olin Lathrop Jan 17 '16 at 13:34
  • There are no other technical details on the box? – jippie Jan 17 '16 at 14:57
  • I wonder where I can find "The Commission Regulation (EU) No. 874/2012 states in Annex VII, part 2.", No Annex VII in the document. – jippie Jan 17 '16 at 15:10
  • Do ah look like ah know what a killer what is? – user253751 Jan 17 '16 at 21:20
  • Monthly electricity bills are in terms of kWh (e.g. $0.30/kWh), so a consumer can easily see the cost of running this light bulb in terms of money per hour (in this case 7*0.03 cents per hour). – Vortico Jan 17 '16 at 22:20
  • 1000h is probably close to how long the lamp in the living room is on in a year. – njzk2 Jan 18 '16 at 02:21
  • 1000 h is [average life expectancy of a light bulb](https://en.wikipedia.org/wiki/Phoebus_cartel). – Trang Oul Jan 18 '16 at 09:26
  • Ironically, this abbreviation is longer than spelling `Watts` in full. – Dmitry Grigoryev Jan 18 '16 at 10:22
  • @TrangOul I bet it's not true for LED lamps anymore. – Dmitry Grigoryev Jan 18 '16 at 10:24
  • As an aside, LEDs in the US do just use W, for the most part (usually with a note somewhere about the equivalent wattage for an incandescent bulb). The actual brightness does seem to be most commonly given in lumens now, however. – JAB Jan 18 '16 at 14:50
  • @JAB: What you're thinking of is the packaging front; it's carrying basically the same information in Europe as well. [See here](http://fastvoice.net/wp-content/uploads/2013/08/Osram-A40-6W-Pressebild.jpg) -- you see "6W = 40W" with appropriate imagery on the packaging front (top-right), and below that the (more accurate) "470 lm". What the OP is talking about is the EU energy label on the right side of the package, which is standardized for *any* kind of electrical appliance. As Philipp stated, the different unit given is probably because `kWh` is what you pay for. – DevSolar Jan 18 '16 at 15:11
  • By the way: This [LED bulb from IKEA](http://www.ikea.com/gb/en/catalog/products/40288066/) consumes 3.5W. Or 4kWh/1000h. (It's just an example, you'll find this very often) This so-called energy label should tell the "dumb" consumer how much power a device needs. That average value is nice for fridges, but it fails for such low-power devices, as it tells him it needs 14% more than it actually does. [Another example showing it's not just due to rounding](http://www.ikea.com/gb/en/catalog/products/10266221/) – sweber Jan 18 '16 at 15:13
  • Another strange thing: The upper right symbols means "Don't throw it into the residual waste bin". The lower right means "Throw it into the recycling bin". While the upper addresses the bulb, the lower addresses the packaging... tztztz – sweber Jan 18 '16 at 15:16
  • @sweber And then there's the 30-degree right angle. DevSolar: I see. – JAB Jan 18 '16 at 15:23

3 Answers3

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Anyone who has a clue about how physical units works will of course realize that kWh/1000h means "1000 watt-hours per 1000 hours" which can be shortened to just W.

But when it comes to lamps, the unit "W" is already used for the light output. Light bulbs which use more energy-efficient technologies than the classical incandescent light bulb often state their light output in equivalency to an incandescent bulb with a specific power consumption. Until 2010 you could often find LED light bulbs stating to be "equivalent to a 40W bulb". So the consumer knows that if they want to replace an old 40W incandescent bulb with an equally bright LED bulb, they need to look for a 40W LED bulb. A consumer buying an LED lamp with an input power of 40W might be surprised by how bright it is.

Also, the average consumer doesn't know much about how electricity works. They know they need to pay for their electricity consumption in a unit called "kWh", so they want to know how much they need to pay when they run the device for x hours.

So from the point of view of the average consumer, the unit "Watt" means "light-intensity" and "kWh per hour" means "energy consumption". A physicist will of course inject that the unit for visible light radiated by a source is "Lumen" and "Watt" is the unit energy consumption should be measured in, so that's what should be printed on light bulb boxes. But physicists aren't average consumers.

Using different units for each - even if both of them are misleading from a physicist's point of view - is what's the least misleading way to communicate it to the end-user.

Philipp
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    That's the "least misleading" until marketing people figure out a light bulb is lit 4 hours a day on average, and invent a new clever unit 1`kWh/year`==0.68`kWh/1000h` – Dmitry Grigoryev Jan 18 '16 at 10:27
  • @DmitryGrigoryev ...and then there is a lawsuit and they need to add a fine-print *Yearly consumption may vary depending on how you use your light bulb. And then another marketing company comes along and realizes they can make their exactly identical product look better when they manage to find a study which says a bulb is only lit about 3 hours a day. – Philipp Jan 18 '16 at 10:36
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    @Philipp They can always start the fine print with "Does not contain asbestos. No animals were hurt during production..." so everyone stops reading before the sentence you mentioned comes up. So yeah, in the end that second company wins. – Dmitry Grigoryev Jan 18 '16 at 10:42
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    People, please, stop giving them ideas... – mikołak Jan 18 '16 at 11:04
  • To be fair, most light bulb packaging that I've seen *does* include lumen ratings, it's just buried in the fine, light print at the bottom. – hBy2Py Jan 18 '16 at 14:09
  • @mikołak I think you might be too late. In the US light bulb lifespan is already measured using 1 year = 1000 hours (2.8 hours/day); and AFAIK the "you'll save $NN a year" (vs incandescent bulbs) marking on CFL/LED packages is based off that usage number. – Dan Is Fiddling By Firelight Jan 18 '16 at 19:36
  • @DanNeely ?? But "you'll save $NN per year" would also depend on something as volatile as local energy prices – Hagen von Eitzen Jan 18 '16 at 20:00
  • @HagenvonEitzen Yeah, I've always rolled my eyes over that over simplification. I believe the fine print says that they use the national average price of [12c/KWh](http://www.npr.org/sections/money/2011/10/27/141766341/the-price-of-electricity-in-your-state); which isn't too far off (50% high to 33% low) if you exclude Hawaii as an extreme outlier. – Dan Is Fiddling By Firelight Jan 18 '16 at 20:11
  • Even though (as stated) most folk don't understand electricity, somehow thy came to understand how bright 40W was. Surely, if the brightness was given in lumens, folk would get used to that terminology, even though most folk don't understand light? – KDM Aug 04 '16 at 16:13
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    Sadly, this is exactly the kind of confused thinking that in my opinion is the cause (as opposed to a consequence) of people not understanding physics. It should be mandatory to display lumens for light output and watts for consumed power and ban all other units. But then again, I am a physicist. – Martin 'Kvík' Baláž Jan 05 '22 at 18:21
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The energy rating covers all types of electrical appliances including fridges, washing machines, etc.

In the case of a fridge the instantaneous current could be zero or full on depending on the thermostat. It makes more sense to put the fridge into a 20°C room, power it up and read the kWh used in, say, 24 h and scale it up. This gives a better idea of the average power consumed by the device.

I agree that this could be quoted as X watts average. On the other hand if I know I pay €0.15 / kWh for electrical energy it is a very simple calculation for a non-technical user to figure out the cost of running the appliance.

Mind your units: 'K' is kelvin. 'k' is kilo. ;^)

Transistor
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    "On the other hand if I know I pay €0.15 / kWh for electrical energy it is a very simple calculation for a non-technical user to figure out the cost of running the appliance." Is it? Tell said non-technical user that it uses 7kWh/1000h and then ask them how much it'd cost a year. – NPSF3000 Jan 17 '16 at 16:14
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    @NPSF3000 Let's just hope that price drops to 0.12 €/kWh and then we can simply state 1 W = 1 €/year :) – jpa Jan 17 '16 at 17:33
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    @NPSF3000 Knowing the number of hours in a year is irrelevant. How many hours is the light bulb on per day? 1000 hours of use could equate to 10 years of minimal use. The fact is that *everything* is rated 'over 1000 hours' and is therefore directly comparable to *everything else*. – CharlieHanson Jan 17 '16 at 17:37
  • I'm not sure if it's just a coincidence, but the nominal lifespan of a traditional incandescent filament lamp is 1000 hours. So the kWh/1000h figure for an incandescent lamp is also the amount of power it would use over its lifespan. – Simon B Jan 17 '16 at 21:17
  • "1000 hours of use could equate to 10 years of minimal use." It could also be 1 year or 100 years, as an average non-technical user, how do I figure this out? – NPSF3000 Jan 17 '16 at 23:27
  • The system is really intended as a simple energy efficiency comparison guide. You compare ratings while in the store and you can select between various appliances based on, amongst other things, their energy rating. A++ is best. E is worst. How many hours a year you run it, if at all, is your business. – Transistor Jan 17 '16 at 23:42
  • You make it sound like `kWh/1000h` has the notion of average, while `W` does not, but they are **exactly the same**. If your light bulb lasted for 999 hours, or 1 hour, or minute, you can still choose to rate it in `kWh/1000h`. – Dmitry Grigoryev Jan 18 '16 at 10:21
  • So a year is 1000 hours? I thought it was pi E 7 seconds ... – Hagen von Eitzen Jan 18 '16 at 20:01
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It allows you to do an easy comparison between different light bulbs, because it is a standardised way of presenting the power consumption of the item.

Chris Williams
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