# Number relations

• Oct 31st 2008, 12:48 AM
Meppso
Number relations
Hi All,

I have a small maths problem. I am trying to create a relationship between two sets of numbers. The non-linear value comes from a light sensor and the other set of values are LUX levels. The values are as follows :-

LUX Value
10, 40800
20, 26500
30, 20400
40, 17000
50, 14700
60, 13020
70, 11780
80, 10750
90, 10230
100, 9320

I have plotted these values out and they appear to give a decaying exponential curve. What I am aiming for is two cells in excel, one in which I can enter a LuX value and the other cell will display the associated ohms value.

Regards,

Andrew.
• Oct 31st 2008, 05:46 AM
HallsofIvy
Quote:

Originally Posted by Meppso
Hi All,

I have a small maths problem. I am trying to create a relationship between two sets of numbers. The non-linear value comes from a light sensor and the other set of values are LUX levels. The values are as follows :-

LUX Value
10, 40800
20, 26500
30, 20400
40, 17000
50, 14700
60, 13020
70, 11780
80, 10750
90, 10230
100, 9320

I have plotted these values out and they appear to give a decaying exponential curve. What I am aiming for is two cells in excel, one in which I can enter a LuX value and the other cell will display the associated ohms value.

Regards,

Andrew.

If (x,y) appears to have a decaying exponential curve, that is if \$\displaystyle y= Ae^{kx}\$, then log y= log A+ kx, a linear relation. You can convert your list to (x, log y) and find a least squares line Y= kx+ b where Y= log y. Then \$\displaystyle A= e^b\$