It's all calculation.
L* is from CIELAB color space, calculated from Y in the CIEXYZ. It is trying to match how lightness in human eyes. Luminous efficiency function V(λ) is be used.
Whiteness is also calculated from CIEXYZ, but yellow/blue tints are considered. It presents how white is a paper. Bluish papers have higher whiteness than yellowish papers.
Brightness's purpose is something like Whiteness, but using a spectral distribution function to calculate it. Brightness mainly considers reflection around 460 nm, OBAs will make huge influence.
There is no simple formula to convert from each other. But you can get your own L*/Whiteness/Brightness from spectral reflectance distribution of a paper white.