Left panel: synthetic spectra of T_eff = 5300 K and log  g = 8 (cgs) helium-rich white dwarfs computed without (solid lines) and with (dashed lines) the IR opacity of helium computed in these studies. The three sets of lines represent the models of He/H = 10⁶ (resembling the pure He spectrum), 10⁵ and 10⁴, counting from top to bottom by taking the values at λ = 20 000 Å. Right panel: synthetic spectra of pure He atmosphere white dwarfs (log  g = 8 (cgs)) computed without (solid lines) and with (dashed lines) the IR opacity of helium computed in these studies. The different sets of lines represent the results for T_eff = 8000 K, 7000 K, 6000 K, 5000 K and 4000 K (from top to bottom). The vertical axis label is identical to that of the left panel.