Thin Film Interference: Finding m Value

[LamyJamy]

For thin film interference, I was wondering how you know what the value of m is for the equations:
2nt/λ=m (destructive)
2nt/λ -1/2=m (constructive)

 

[jtbell]

It depends on the problem you're trying to solve. In some problems, all values of m give valid solutions, so you have to give a list of possible solutions. In other problems, there are constraints that restrict the acceptable values of m. For example, it might be required that the wavelength be within the visible range (about 400 to 700 nm).