Wattage is referring to two things: power and radiant flux. Radiant flux is the sum of all electromagnetic radiation coming off of an object. Which is technically also power, but in a different form. Electromagnetic radiation, instead of electron flow.
For incandescent lights, this is very simple. A filament converts power to radiant flux using resistance. Electron flow becomes heat+light+other em radiation, which is radiant flux.
Since filament performance was pretty universal, you could use wattage to accurately estimate light output.
However, with the discovery of other forms of light, like, for example, LED, things changed. An LED is much more "efficient" (if the goal is light, an LED is a terrible source of heat compared to a filament), and gives off more of certain types of electromagnetic radiation, and less of others. So, less heat, more light.
So, they came up with a new unit, the lumen. Lumens measure luminous flux, i.e. only the visible light band of the EM spectrum. Useful for lights, since that's the point of a light.
But the old system still kinda stuck around. Like how you can go to the store and buy a "60W" LED, which actually pulls like, 9W of power, but gives off the same luminous flux as a 60W incandescent would have. Technically this should be expressed in lumens, but old habits due hard.
So, I'm guessing your 1000w bulb that consumes 100w is giving off the light equivalent of a 1000W incandescent bulb, but only using 100W of actual power.
This is somewhat oversimplified to the point of probably not being 100% correct.
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koraks said: So there's really no quick & dirty way to equate X Watts of LED power to Y Watts of some other form of lighting.
I mean...Watts is the "quick and dirty" way--because Watts can be used to measure the electromagnetic flux coming off a bulb.
To go back to my example of incandescent vs. LED bulb--filament are extremely efficient at converting electrical power to blackbody radiation, which is also a form of power. But it's very non-specific. So, 60W incandescent is giving off like, 50W IR and lower energy flux, 9W visible flux, and maybe 1W high energy wavelength flux. A 60W "equivalent" LED consumes 9W electricity and gives off 9W visible flux.
Hence, to the "quick and dirty" measurement of visual comparison, a 9W LED is the same as a 60W bulb.
But you're correct in that this breaks down for grow lights and such, since plants don't use human visual spectra.
(pretty sure we're saying the same thing in various ways with varying amounts of detail, but that's okay because this discussion is meant to...illuminate...the subject for anybody that's passing by with a question!)
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