Grid of constant-density PDR models for varying external FUV radiation fields but fixed n_H = 10⁷ cm⁻³ and x_C = 1.4 × 10⁻⁴. Colored curves show the predicted line intensities of the neutral carbon lines discussed in the text relative to the line intensity reference model (G₀ = 2 × 10⁴). While the NIR carbon line intensities increase with G₀, the [C I] 609 μm line intensity is much less dependent on G₀.