Pretttttty stoned but I have a legit lighting question(I hope)

So I'm just reading over stuff, I haven't posted on here much, but I love growing, and have been trolling these boards for a while (Coming out with a vert Scrog Arjan's Haze#2 grow journal soon!), found something that didn't make sense to me.

Don't feel like quoting this sticky properly so I'll just cut and paste this from some thread about what to know about lighting, also I've seen this on many sights while I've been growing :

Determining lumens for your grow area:
Determine the square footage of your area (example in a 4 foot by 4 foot area, there is 16 square feet)
If you have a 1000 watt High Pressure Sodium, that produces (approx.) 107,000 lumens.
Divide this by 16 (your square footage) 107,000 / 16 = 6687 lumens per square foot.
So just divide the total amount of Lumens, by the total amount of Sq ft, and thats your lumens per square foot.


The thing I don't understand about this, the reason this doesn't work for me is that if you are using a 1000 w hps bulb, still producing 107,000 lumens, on a 2x2 foot plot, which is 4 sqft, that woud be somewhere around 27k lumens per sqaure foot.

So my thing is, isn't it distance from the light that matters, not grow plot area, also what are the differences in lumenocity (hahaha is that a word? I feel like I made it up) varying by distance from the light. I know 400watt should be 18-20 inches away, but what are the cold hard numbers in lumen intensity by how far the bulb is.

Check out this link. It might contain the answers you're looking for: YOR - Lighting Resources Notice the inverse square law for light intensity. There's lots of good reading on that site. I can't vouch for the accuracy of all the information there but it seems legit.

I would assume that most guidelines for recommended lumens or watts per s/f assume an "appropriate" distance between the light and the plants. And sort of the same with "Determining lumens for your grow area". A simple lumens divided by s/f calculation can't determine how much light your plants are actually receiving since as you've pointed out, there are other factors--distance being a huge one. I'm sure reflector efficiency and the presence/absents of wall reflectivity are significant too. But perhaps "Determining lumens for your grow area" retains some usefulness for making generalized and comparative conclusions about how much light is available in a grow setup. I'm new to this whole game though so don't take my word for anything.