The prediction of the ultraviolet-visible spectra of C-40 hydrocarbon carotenes and C-20 retinals has been made by molecular modeling using the density functional B3LYP in the Spartan molecular modeling software. After geometric optimization the LUMO-HOMO transition correlates well with the published ultra-visible spectral maxima and explains the spectral shifts seen in cis-trans isomers. The comparison of the calculated structure cis and all trans retinal to the crystalline structure shows a high degree of correlation.