Lighting Question

[say-g]

hmmm i remember seeing an expression on plugin cafe somewhere that changed the light colour or somthing, seemed quite handy, anobrin had some changing lights in his stargate animation, http://www.cgtalk.com/showthread.php?s=&threadid=21141

oh yer an that expression is called pulsar

hope this is of some help to you

[Per-Anders]

without seeing what you're doing... you're breaking the laws of physics. what you need to do is add a little red & green to the mix, just a tiny ammount (of the curtain), and maybe the tiniest ammount of blue and green to the light. the thing is if you shine a red light into a scene (pure red we're talking here) only the red component of any object's material will show up (reflect the light), so by trying to light up a blue curtain (which contains no red) with a red light (which contains no blue) you get nothing, just black. they have to have some colour in common (just a small ammount will do) otherwise you wont get any light reflected.

you have to remember that in the real world you simply dont get pure light or pure pigment, so a red spotlight contains a lot of the rest of the spectrum, and blue cloth also contains the other primary colours to a degree... thus in the real world you get a normal red spotlight and a bit of blue cloth, chances are you will end up with a dark purpley thing (the purer the colours the darker the end result). but in the computer you can shine pure red light on a pure blue cloth so there's no red component to reflect in the blue cloth (i.e. it absorbs everything apart from the blue).

[LucentDreams]

Originally posted by Linds
I've got a little lighting niggle I'm hoping someone here might know the answer to.

I've got a backdrop, a curtain actually, in a scene, lit by a couple of spots. Think theatre lights, The spot color is white, at the moment, but at some point in the animation I want the lights to turn red.

Now my problem is this. The curtain is a dark blue. The white lights give a nice pool of bright blue light, falling off to darkness at the edge of the frame, pretty much as you would expect.

But, when I change the color of the spot to red, I get no illumination at all. I expected to get a red/purple spot of light on the curtain, but nothing. I've tried cranking up the brightness of the light to several hundred percent, but it doesn't seem to make any difference.

Am I trying to break the laws of optics and/or physics here, or am I missing something obvious.

Thanks folks.

Linds

In a way, yes you are, Think about it this way, A blue material absorbs red and green light but relfects blue light. A redlight (255R 0G 0B) Cast no blue or green so, the only thing you would see is the specular highlight if was white, wwhich in the render would be red as all there is to reflect is red.

Heres an example to think aobut using the ol red and ble makes purple. A blue room, all the walls the same blue, with a white light on top (like a cornell box) Place a red ball in the center underneath the light. Use radiosity to simulate real world lighting, and waht will you see. the top will most likely be red correct? The bottom of the ball will be what? Purple right? Well no, its still red, there is more blue light than the red material absorbs however, which is what makes us see purple.

At night everything seems black mainly because there is little to no light to refelct back, what little light there is, is mostly absorbed.

Hope that makes sense.

So what is the solution to your problem? Don't use a solid red light. I always select the colour I want, (in the colour picker window) and the mosey on over to the brightness slider (in the colour picker window) and bring it up to 75 % is I want a darker more saturated lighting, and 85-90 if I want brighter cleaner lighting. You'd be amazed how red a scene can get from waht appears to be a pink colour (remeber Pink is still in acutality red. The brighter colours like red and yellow tend to noticably change when made brighter (in reds case) or darker (in yellows case) giving you Pink and Brown.

[Linds]

mdme_sadie & Kai,

thanks for two very lucid and er.. illuminating (and compatable) explanations. Kind of makes you realise how much you've forgotten since you left school. Once you explain it, it all makes perfect sense.

I'm off the the Cinema lab to experement with my new found grasp of science.

Thanks for taking the time to answer both.

Cheers

Linds

:beer:

[LucentDreams]

LOL its not always that MDME Sadie and I agree so you know when we do it muct be right ;)

[Per-Anders]

LOL, we love each other really! We just have... erm... professional... um... discussions with each other! on certain subjects... lol

[LucentDreams]

Professional disagreements ehh yeah thats it, we should be producer and director on something really we'd do great :D

[Per-Anders]

ah one of those projects that barely get started let alone finished! hmm. yeah, i suspect we'd could be good at those working together. :D lol

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