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Historically, incandestent light bulbs were marketed primarily by their power consumption in watt. I don't know if light output in lumen was specified at all. I'm not aware of any other electrical good sold primarily marketing power consumption: it's listed in the specifications, but it's never the primary selling characteristic. Loudseakers may be sold based on power in watt, but I believe that refers to useful power output rather than power consumption.

Now that lights are mostly based on CFL, LED, and other techniques, it has become standard to specify light output in lumen. Considering that light output is the obvious primary characteristic of any light source, why wasn't lumen used from the start when characterising any kind of bulb?

(There are even packages that show the hypothetical power consumption for an incandestent light bulb with the same light output!)

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    $\begingroup$ I would assume it was simply because power consumption is easy to measure with an ammeter, but light output is very difficult to measure, especially with high precision. $\endgroup$ – Ben Crowell Jul 29 '16 at 19:24
  • $\begingroup$ Wattage tells you the cost of operation, and from the total wattage on a circuit you can determine the current, and hence the limits for a particular circuit are easy to figure - the fuse limit in amps. In the early days the electricians would figure this for you when your home was electrified. Lumens are for lighting engineers. $\endgroup$ – Peter Diehr Jul 30 '16 at 10:31

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