Luminescence and excitation spectra of a Langmuir-Blodgett multilayer with a high concentration of densely packed perylene chromophores are measured at 2 K. They are compared with corresponding spectra of the dimeric alpha-perylene crystal and of perylene dimers formed in a glass. The majority of the perylene chromophores are arrested in We Langmuir-Blodgett film in the form of open metastable dimer configurations with monomer-like spectra. They dominate the absorption spectrum and excitation spectrum of luminescence. From these open dimers the excitation energy is rapidly transferred to the lower excited state of a stable dimer species functioning as a trap. Luminescence from this excited g-state leads to the peak at 550 nm in the luminescence spectrum. A second peak at 630 nm and the red side of the luminescence spectrum are due to E-excimer luminescence. The wide spectral range of the luminescence, extending from below 500 nm up to 800 nm, reflects sub-angstrom differences in the configurations of the dimers.