Due to the combination of high radiation densities in the BLR and the high column densities of clouds which are optically thick to the Lyman continuum, many lines emitted from the BLR are likely to be optically thick, and hence will be emitted anisotropically. Ferland et al. (1992) discussed the case where the amount of anisotropy is constant for all clouds, but in reality the anisotropy will vary for a spatially extended BLR, depending on the local physical conditions. To study this effect, we have computed several models for spherical BLR's populated by an ensemble of spherical clouds in pressure balance with an intercloud medium, using our BLR modelling code, PROSYN (Goad, O'Brien & Gondhalekar 1993), which utilizes the photoionization code CLOUDY (Ferland 1991). Here we show some of the results for a constant pressure BLR model, where the cloud density (N) and column density (Ncol) are constant with radius (r), and hence the ionization parameter (U) varies as r−2. The model was normalized to have N = 1010 cm−3, Ncol = 1023.75 cm−2 and U = 10−2 at a radius of 10 light-days. The inner and outer radii were set at 0.3 and 56.2 light-days respectively, giving a range in log U from 1.0 to −3.5.

The total line emissivity εtotl = εin + εout, where εin is the emissivity of the inward cloud face (towards the ionizing continuum source) and εout is the outward emissivity (away from the ionizing continuum source).