Not sure I aren't an expert, but considering his test sources "pointed at a white card or sky illuminated by sunlight" and "four emission lamps with daylight spectrum [reflected sunlight] for comparison" also noting all the primaries are there. I would think this is in the visual spectrum. Anyhow why filter out what you cant see anyways, probably why folks dont use an IR filter for visual observations, because we can see in IR

Perhaps someone else has a better answer.

regards,CS