[Brightcolours]

That is the wrong test. Our eyes are useless at determining spectrum which is what matters here. The best test would be to take the same photo with and without a known effective UV/IR block filter. My argument is that you wouldn't see a difference, whereas if you are right, you would.

 

Alternatively you could try using a "clean" light source so there is no UV or IR to detect. Apart from direct sunlight, I don't think there are any significant sources of UV in normal lighting. So using artificial lighting for example as a substitute may eliminate that, but there may still be an IR component depending on the light source. Ever tried IR photography? For practical purposes, of lighting you're likely to encounter in a domestic environment, only incandescent bulbs really put out much photographic IR. Fluorescent and LEDs are pretty clean there.

That makes little sense... If a red flower in the same sunlight looks the same as a red object, and one makes a photo and only the flower poses a problem, then it is an "invisible" spectrum problem. No need to use a different light source to determine that issue. Note that not all red flowers are problematic. It depends strongly on kind and variety. A red anemone or poppy are just fine to photograph, dark red velvety roses are nearly impossible.

Same with blue/violet/purple flowers. Some are easy to photograph, others even make patterns appear on photos that were not "there" when seen with the eyes.