Dear Teacher,

I found the idiomatic phrase, "fall short of," is used with the specific numerical value. Is it appropriate to use "fall short of" to describe that some value does not reach a given point?
i.e. It happens ... when the wavelength falls short of 300 nm...

If so, in the above example, 300 nm is included or not?
Does it happens when the wavelengh is 300 nm or 299 nm?

If not appropriate, what is the better expression instead of "fall short of some value"?

Thank you for your help.