One good thing is that the lens does not have to have a filter when doing this. The other good thing is that since you have a constantly-powered and constantly-colored light source, exposure is much easier to nail than with natural light. It would be fairly easy to determine a good GN and EI. Sunpak makes an IR head for their GN 200 622 model. I am not sure how much punch it puts out compared to its white light output. Many of the classic Wee-Gee pix were made this way, using IR flashbulbs.