https://doi.org/10.1351/goldbook.F02361

Logarithm of the ratio of two values of a field quantity, usually amplitude. Levels are expressed in different ways: LF = ln(F/F0).Np, where N p is the symbol for the unit neper coherent with the SI, or LF = 20.log10(F/F0).dB, where dB is the symbol for the unit decibel.*Source: *

Green Book, 2^{nd} ed., p. 79 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)

Green Book, 2