Effect of incident radiation on helium line intensity across a section of a cylindrical thread. The frequency-integrated intensity is measured in erg cm^-2s^-1sr^-1. The position is given in fractional units of the cylinder radius. The horizontal axis represents the position vertically away from the solar surface with the zero point at the thread centre. The left-hand graph used the p4 model, whilst the right-hand graph used the isothermal t1 model.