Lumens sq/ft and Sun lumens sq/meter

Since I've added 400w to the 150w I've been trying to figure out what my lumens at plant canopy was roughly. While I was reading up on inverse square law and I am slightly confused; I used rough estimate of 71,000 lumens at 21 inches n 23 inches away from plant canopy, divided by 4 for 2x2 area (still small plants), then took the 17,750 lumens sq/ft and times by .25 for 1/4th intensity at 2 feet away, my final estimate came out to 4,437.5 lumen sq/ft using init lumen output ratings ect, quite short of my 7-10k desired lumen output; however the confusing part is after reading this on wiki:

For example, the intensity of radiation from the Sun is 9126 watts per square meter at the distance of Mercury (0.387 AU); but only 1367 watts per square meter at the distance of Earth (1 AU)—an approximate threefold increase in distance results in an approximate ninefold decrease in intensity of radiation.

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Does this mean 1367 watts per square meter (3 feet by 3 feet) and 93 lumens per watt for sunlight = 127,000 lumens over a 9 foot area for the sun??? Lol? I failed math class just as a disclaimer but wtf.

So is my estimate of 4,500 lumens sq/ft accurate estimate? Also is this accurate estimate of lumen output of sun?

Haha I think you blaze to much.....

Indeed; dually noted. Just trying to figure out what my plants were getting and what natural sunlight was giving. :'c

Just jokin bout your name bro.. Google it , I had the same question a couple weeks ago forgot what it said though. Just Google sun lux or something to that extent

Alright for real though Google "daylight" Wikipedia it tells you the amounts under specific conditions Its safe to assume bout 50,000 lux

lol o gawd converting lux to lumen over a desired area T_T

im going to assume my estimate of 4,000 lumens for 550w hps at 2 feet is roughly accurate, hoping someone will come in and correct or confirm. tnx though.

From what I understand, 10,000 lumens per square foot is optimal. But I know people that grow with as little as 5000 and less. Don't stress it so much, I know I was but after I started I found it was not as hard as I thought. IF anything get yourself a light rail if the area is wide. It will move the light(s) back and forth and give all your plants an even amount of light.

I am currently growing with just under 8,000 lumens per square foot, but have had success with much less.

7k is optimum. No more than 10 the sun does about 7. Too much and you'll start bleaching. An hps puts out more than the sun at the top of canopy over 600 watts

from a quick google search:


Minimum amount of lighting needed is around 2000 lumens per square foot.
(Two – 23 watt CFL’s, per square foot*)


Mid range is around 5000 lumens per square foot.
(Three - 23 watt CFL’s, per square foot*)


Optimal is 7000-7500, or higher, lumens per square foot.
(Five – 23 watt CFL’s, per square foot*)

Yeah I seen topfuels post about the optimal lumens thats why i wanted to get in 7-10k range, but when i started doing the math I realized with 550w I'm still 3k away from 7k optimal, Its ok though I'm not planning on increasing lighting for 3 plants anyhow.

You can bring the lights closer and you will be just fine, just make sure you're cooling that light. I have a 450CFM intake fan blowing trough my lights, and I also have a standard house fan blowing up towards the glass on the my lights. That last bit alone dropped the temps around 4 degrees.

Temp won't stop bleaching. A 16 dollar box fan puts out a lil over 2000 cfm.. if running 71,000 lumens (rated at 12inches) its very possible if you go too low... but in a 2x2 space? You have plenty of light unless over 4ft. The sun at full blast is 100,000lux that's lumes over sqft so the sun won't do more than 10k lumens that can bleach some sensitive plants.