So I’ve been trying to do what I’ve read is impossible in blender, just out of sheer boredom… I kinda got a little bit going, but Im curious as to why it goes R Y O G B I V, instead of the normal R O Y G B I V? All I’ve used was 3 suns, of Red, Green and Blue. A glass material right against the camera, and a cube with default material and some transparency.
What do you need three Sunlamps for, they would all affect the whole scene unless some areas are shadowed.
Would you get the same effect if you used one Sun with very soft shadows and a red, green, and blue glass plane behind the camera?
Nope, not getting the same effect no matter which way i do it.
You are getting this effect cos the object throwing the shadow is more transparent around the edges than in the middle, thus, looking from the top, you have a red patch, then suddenly lots of green light, so the image goes yellow. Then the green fades out as the centre of the object approaches, so the colour turns back to orange, and so on.
To do a rainbow in Blender I would use a smoke or particle system to project the image onto, then use the project option in the light to put a painted image of the rainbow itself onto that.
To do what you are trying to do, you need to use four lamps (2 red, one green and one blue), with a single plane between them and the target. That plane needs a band of transparency, that fades linearly from solid to transparent and then back. It has to be placed so that the exact edge of the band of one colour lines up with the centre of the next, so that they overlap perfectly. They need to be sun lamps, or the colours will get messed up except in the middle of the image.
Matt