Synthetic model-atmosphere spectra for the WNLh star F6 computed for two differing assumed interstellar reddening laws, illustrating the dramatic dependence of bolometric luminosity on this choice. HST photometry employed are from Table 1, Fi02 and Dong et al. (2011). The black line reflects the model spectrum that was reddened with α = 2.34 whichresults in A_ks = 1.860, while the blue line follows Moneti’s law with A_ks = 3.475. Transmission curves for the filters used for the fit are shown in green (broad band) and pink (narrow band), and symbols are plotted for each magnitude measurement to show the goodness of fit: orange diamonds for the α-model and pink stars for the Moneti model. The x-axis position of each symbol corresponds to the classical λ₀ of the filter at which the zero-point flux is defined. The y-axis position coincides with its corresponding model curve if the observed magnitude matches the magnitude of the reddened model. Although the models differ considerably for Logλ <4.1 (e.g. the F110W filter), they yield the same observed magnitudes. The reason for this is that, due to the high extinction, the reddened-SEDs fall off very steeply as lambda decreases and as a result the effective wavelength of the filter moves to the red.