The idea is to direct all of the nanotube-emitted light onto the PV cells, so hopefully you won't see anything. Citing the Rice article:

> Because electrons in nanotubes can only travel in one direction, the aligned films are metallic in that direction while insulating in the perpendicular direction, an effect Naik called hyperbolic dispersion. Thermal photons can strike the film from any direction, but can only leave via one.