I shot a small stage show earlier this week where LED projectors were casting splashes of colour on black curtains. Each projector was formed of about 100 (I'm guessing here) large LEDs evenly distributed as red, green, blue and white. Colours were combined to make other colours (i.e. red and blue for purple), but the red LEDs never showed up on cam, not even when mixed with other colours (purple showed up as blue).

I'm guessing this has to do with the limitations of video, but is there a way to get a red projector to show up on cam? Is this only a phenomenon with LED projectors?

Jaques,

In most cases, modern cameras are PARTICULARLY sensitive to light at the red end of the spectrum.

(For a fun experiment, take a consumer camcorder and point it at the business end of a typical remote control and gaze in wonder as you can suddenly "see" the flashing control beams in action!)

Because of this sensitivity, some cameras have IR FILTERS in place to remove the excessive IR content from scenes.

I'm wondering if your problem is that you have a camera with a overly robust IR filtering in place, that's impinging on the visible red light spectrum and keeping your camera from recording the wavelengths of the LED array properly?

Just a guess here.

It's a Canon XH-A1, I hadn't heard until now of problems it might have over-filtering IR light...

EDIT: actually, now that I remember, I was using a preset to bring out flesh tones, maybe it also inadvertently filtered IR.