How can the Airy's equation $y'' - xy = 0$ be used to model diffraction of light?

Differential Equations with Boundary-Value Problems by Dennis G. Zill, Michael R. Cullen states that the equation is used to model diffraction of light. It doesn't explain how, it just goes on to solve it using a series solution.

Has anyone any idea how it is used or has any references? Or if anyone knows any other applications of this equation then that would be interesting also :)

• A survey of other physical applications of Airy equation can be found at: dlmf.nist.gov/9.16 :) – shamisen Nov 19 '17 at 17:54