The solvent polarity parameter E-T(30) is newly measured from the solvatochromism of the betaine dye 30 for 84 solvents and re-measured for 186 additional ones. The results are organized in a database. It is shown that the validity of linear solvation energy relationships used for the determination of secondary E-T(30) values is limited to non-hydrogen-bond donor solvents. Relationships with the chain length n are given for the determination of tertiary E-T(30) values of the homologous H(CH2)(n)Y solvent series. The parameter E-T(30) is orthogonal to the function of the refractive index (n(2)-1) / (2n(2) + 1). For non hydrogen-bond donor solvents, this allows to enter E-T(30) as an almost pure electrostatic parameter in a new linear solvation energy relationship. Copyright (c) 2014 John Wiley & Sons, Ltd.