Fluorescent, iridescent, interference, and metallic colorants are part of a modern artist's palette. These materials produce colors far exceeding conventional absorbing and scattering colorants. Current encoding spaces, even so-called wide gamut, cannot accurately encode such modern materials. A new encoding space, ETRGB, has been developed that extends both chromatic and photometric dimensions. ET is an abbreviation for Extended Tristimulus. The chromaticites of the space are the apices of the 1931 xy chromaticity diagram. The photometric range is from 0 – 2 luminance factor, 0 – 130L*. Its white point is CIE Illuminant D50. Nonlinear encoding is based on CIE L*. The extended photometric range is equivalent to 15-bit encoding when compared to current systems. An imaging experiment of an interference-pigment coating demonstrated its usefulness compared with ProPhotoRGB.