The sample inverse autocorrelation function (SIACF) plays much the same role in ARIMA modeling as the sample partial autocorrelation function (SPACF) but generally indicates subset and seasonal ...

Any function and its inverse are symmetrical about the line\(y = x\).

For each distance of the plant from the lamp, light intensity will be proportional to the inverse of \(d^{2}\), \(d^{2}\) meaning distance squared.