Sorry I'm not very good at math, but doesn't the curve show it's exponential? Linear dropoff would be a straight line?
Yes but I stated in ranges..
The intensity of light radiating from a point source is inversely proportional to the square of the distance from the source; so, an object (of the same size) twice as far away receives only one-quarter the light in the same time period.
so let's take the ATI at 15 and 30 inches
138 @ 15" so should be 34.5 PAR at 30"
Chart says 60.....almost 2x the expected.
Also like this (see green lines on brown curve) Like the slope of the curve at different ranges:
See tanks don't exactly let down-welling light out that easy..
unlike free space so it throws off the calculations.
Take reading at 12" and divide by 4.. see how well it matches par at 24"
Maybe I'm looking at it the wrong way but point is we have tanks that behave more in a linear fashion than log BUT each has errors....
If you use 6" and 12" the PAR is more 1/2 than 1/4..
1/4 of 45 = 11.25 Measured.. 21 ect. ect..
go bigger..
6" 12" 24"
45, 11.25, 2.81
real;
45, 21, 7
1/2
45 22.5, 11.25
suppose it's sort of an odd way to look at it..
2x the distance 1/2 the PAR..... Linear probably isn't THE correct term..just smoother than expected.