Comparison of SN 2007J and our N1def models with 0.01%, 0.22%, and 36% helium abundances. Spectra have been normalised to the median flux between 5000 Å –7000 Å. The spectrum of SN 2007J is estimated to lie between +6 and +46 days after V-band maximum and has been corrected for galactic extinction only. Our N1def model is shown at +15 days after bolometric maximum light. Panel a: shaded regions represent He I λ5876, λ6678, λ7065, and λ10830 at rest and blue-shifted by the maximum velocity of the model (∼8800 km s⁻¹). Panels b–e: zoom-ins of the regions surrounding He I λ5876, λ6678, λ7065, and λ10830, respectively. Panel c: host subtracted spectrum. Rest wavelengths are denoted by a vertical dashed line.