Okay. 53,000 lumens divided by 2 foot squared (53,000/2x2) which is 13,250 lumens at the plant tops.
thanks for this formula
Actually his math was a little off as well.
may add that I keep my HPS 16 inch`s away from my tops ... 18-22 inches to most tops though ..
and I had 6-7K foot candles at my very top .. most tops had around 5K .. bottom growth had around 2-3K
dont have that device yet. but thanks for the link slipon. i know this is an old thread. im new here and just lurking around
learning many thing from the site before i start my first grow this year.
this is to shed more light on Inverse sqr law..
i tried to compute the lumens output of a hid just like the one you posted.
i noctice from the post
footcandles = lumen/10.75
lumen = fc*10.75
12inch or 1ft distance of 600hps is 92000 lumens or 8.52k footcandles
20inch or 1.66ft distance of 600hps is 55200 lumens or around 5k footcandles based in Slipon Post
Formula i think in inverse sqr law for hid is:
l
umens based on distance =
HID lumens*(12 inch /
distance in inch)
cause in 12 inch or 1ft the rating of hid doesnt drop based on light tester i think
eg1:
HID 400w = 50000
Distance in inch on light test to HID = 12 inch
lumens based on distance = 50000*(12/12)
lumens based on distance = 50000*(1)
lumens based on distance = 50000 lumens on that distance of 1 feet or 12 inch with the area of 1sqd.f or 144sqd.inch illuminated light
eg2: based on siphon light meter
HID 600w = 92000
Distance in inch on light test to HID = 20 inch
lumens based on distance = 92000*(12/20)]
lumens based on distance = 92000*(0.60)
lumens based on distance = 55200 lumens or 5134 fc on that distance of 1.66 feet or 20 inch with the area of 2.77sq.f or 400sq.inch illuminated light
the further the light the less lumens/fc and greater area if illumination[/CODE]
IF my assumptions are right the he uses 600w hps and a reflector hood then this is right
Inverse sqr law doesnt apply on reflected light
we can all estimate the lumens with just a ruler.