Where is fringe spacing measured from with white light?

[CAH]

Fringe spacing is the distance between two adjacent maxima or minima.
For white light, is a maxima the distance from red to red (green to green, blue to blue..)? or the middle of the maxima to another middle of another maxima (i see that this distance will be the same since its middle to middle or end to end but still), does it matter?

 

[sophiecentaur]

No, it doesn't "matter" as long as you can really identify the maxima or minima in the presence of the other wavelengths. That's why people tend to use monochromatic light. You could always observe the white light interference pattern through a colour filter, to eliminate the effect of other wavelengths.