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3.1.4. Optical

The use of standard line diagnostic diagrams (e.g. Veilleux & Osterbrock 1987) show that three of the five ULIGs have Seyfert spectra. Both ULIGs with Seyfert 1 optical and/or mid-infrared spectra have LBLR/Lbol ratios nearly identical to the mean observed ratio for UV-excess QSOs, consistent with the hypothesis that the bulk of the bolometric luminosity in these infrared-dominated objects may indeed be due to a dust-enshrouded UV-excess QSO.