Anyone understand lumens in relation to wattage of a light?

If a light source emits one candela of luminous intensity uniformly across a solid angle of one steradian, the total luminous flux emitted into that angle is one lumen (1 cd·1 sr = 1 lm). Alternatively, an isotropic one-candela light-source emits a total luminous flux of exactly 4π lumens. If the source were partially covered by an ideal absorbing hemisphere, that system would radiate half as much luminous flux—only 2π lumens. The luminous intensity would still be one candela in those directions that are not obscured.

The lumen can be thought of casually as a measure of the total "amount" of visible light in some defined beam or angle, or emitted from some source. The number of candelas or lumens from a source also depends on its spectrum, via the nominal response of the human eye as represented in the luminosity function.

The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread. A flux of 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. Mathematically, 1 lx = 1 lm/m[SUP]2[/SUP].

A source radiating a power of one watt of light in the color for which the eye is most efficient (a wavelength of 555 nm, in the green region of the optical spectrum) has luminous flux of 683 lumens. So a lumen represents at least 1/683 watts of visible light power, depending on the spectral distribution.

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I have been trying to understand this quote if you could have a second to help me, I would be grateful and give rep. Mainly the green part highlighted is what I have questions about, does anyone understand how this 1/683watts = 1lumen differentiates between spectral distribution, im assuming since HPS and LED have different distributions, that would mean any attempt to match lumens output for a side by side grow would be useless? Basically since I don't intend on matching LED kwh to that of a 400w hps kwh, I would rather try to match lumens output and see how the grow quality and yield differ. Thanks for your time and considerations, I hope someone has a little better understanding of the "distribution" and how much wattage I would theoritically be looking at for a LED to match the lumens of a 400w (assuming general lumen output is near 40-55,000 for this range of wattage). I tend to have a problem finding any lumen output charts or specs on LEDs also..

edit:
source wikipedia - lumen (unit)


edit#2:

hmm I'm seeing lumen/w at 100-150 for some hps, and l/w for generic LEDs about 95-100? so in a really rough conversion it would be about 25-26,000 lumens for 270w of generic LED?? I hope I'm not misinterpreting this..

um, I have no real idea. But this chart might be of some use to compare lights. http://www.optimalled.com/resources-watt-conversion-chart.php

Yeah that chart seems to follow the general consensus on avgs of lm/w rates, just seems to be a wide open range but apparently it wouldn't take much to match lumens of hps.

just a rough estimate of avg
hps: 110lm/w at 400w = 44,000 lumens
led: 95lm/w at 400w = 38,000 lumens

ofcourse those are just rough avg estimates that aren't really accurate, =/ I guess I'll just try to get as close as possible in lumen output to match the grows.. tnx neway. It seemed to me that the lumen of hps would have been significantly higher but I'm kind of seeing a flux between avg charts ratings, pretty much depends on quality of the lights as well among other variables.

why do you need to know such information anyways? every light you purchase has a lumen rating and this info doesnt seem useful at all off the top of my head cause some bulbs have higher lumen output such as leds, hes also stating if you have a 1 watt light that produces 638 lumens that a single lumen is 1/638th of a watt, his conversion is just an example and shouldnt be applied to figuring out lumen output, you should get a lumen/lux meter as itll give you the best reading, also reflectors play a part in output so get some good ones, if your real serious abxout this i recommend getting a good meter and a yard stick and measure lumen drops every 1/2 inch and temps readings after a hour or so to calculate best distance, also measure lumen output over the area and not directly beneath the bulb as putting tthe light closer can increase lumen output in a specific area and it can reduce it in other spots, so try to get atleast get a decent average all over your area and not just the center.

sorry for run on paragraph lol.

woops,thought you were just gonna try to calculate lumen output by just looking at bulb, but ya still what i said onwards of useless information.

I will check ebay, thanks. I was just trying to figure out how much LED wattage I would need to buy to be closer to the 400w hps without having to purchase extra 100$ unit if I didn't need it but I should be ok once I get a meter that can measure the initial output of the 135w alone at the approx range of the plants growth area.