110505-1332 EDT

Assume the maximum voltage difference between the brightest and dimmest lights is (120-115)/120 = 4.2% and the lamp current is constant and the same for each lamp, then the solution is moderately simple. The voltage drop to the first lamp is V1 = N*I1*R1 where I1 is the current to one bulb, N is the total number of bulbs (assuming all are identical), and R1 is the resistance from the voltage source to the first bulb. The voltage drop between the first bulb and the second is V2 = (N-1)*I1*R2 where R2 is the resistance between the first and second bulbs, etc.

What do you do with the return path? This doubles the voltage drop if the supply and return wires are the same material and diameter.

If you progressively change wire size and bulb-to-bulb distances, then the individual Rs have to change between segments.

If you change the wiring topology from two parallel wires to a three wire scheme, then you can more easily reduce light intensity variation.

You could create a spreadsheet to do the calculations.

See my photo P9 at

http://beta-a2.com/EE-photos.html for an approximation of lamp intensity vs voltage.

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