Z Lighting Falloff or faking it with distance-based brightness/contrast?

[N***@adobeforums.com]

I'm having some trouble getting a light to fall off in the distance. Layers behind a light seem to receive the same amount of illumination no matter how far away the layer is in Z space. Is there something I'm missing?

If that's a limitation of AE lighting, could I fake falloff with an expression to decrease brightness based on the distance from the layer to the camera?

Here's the old Opacity to Camera Distance chesnut:

startFade = 500; // Start fade 500 pixels from camera.
endFade = 1500; // End fade 1500 pixels from camera.
try{ // Check whether there's a camera.
C = thisComp.activeCamera.toWorld([0,0,0]);
}catch(err){ // No camera, so assume 50mm.
w = thisComp.width * thisComp.pixelAspect;
z = (w/2)/Math.tan(degreesToRadians(19.799));
C = [0,0,-z];
}
P = toWorld(anchorPoint);
d = length(C,P);
linear(d,startFade,endFade,100,0)

How would I modify that to work on the Brightness/Contrast plug-in? Is there a better looking way? Exposure plug-in maybe?

[S***@adobeforums.com]

Unfortunately there is no falloff property for AE lights.
I guess the difficulty in replicating the falloff would depend upon whether or not you wanted exponential, linear (or other) falloff.
As for how to achieve that with expressions, I have no idea.
:)

* enter the expression gurus*

[D***@adobeforums.com]

Maybe this will help:

<http://www.motionscript.com/design-guide/falloff.html>

Dan

[Todd Kopriva]

Dan has already responded, so this doesn't add much. But, I wanted to point out that there's a "Simulate light falloff" <http://help.adobe.com/en_US/AfterEffects/9.0/WSAB474311-4B4C-4d54-8887-0F6459F25206a.html#WSF9E27E6B-AC71-4dd8-8135-BE2D08DA77A1> section in After Effects Help on the Web. So far, the section consists primarily of a link to Dan's website. ;-)

[N***@adobeforums.com]

Great! Thanks everyone.

I did a test plugging in the original expression into a Brightness/Contrast plug-in and changed the end number to 0,-100 and it worked just OK.

Dan's solution is much nicer looking!

[S***@adobeforums.com]

Wow Dan.
You never cease to amaze.
:)

[N***@adobeforums.com]

Hey Dan!

I'm using your expression, but I notice I have to use very very small decay amounts to get the right result. For my particular setup, I'm using a value of .0005. The expression slider I have it linked up has a range of 0 ~.001. The slider only displays to the hundredths decimal, so I get something very odd like this:

<Loading Image...>

And if I accidentally slide it into a zero or negative value, I get a divide by zero error and all my expressions turn off (which I can't undo).

Is there any way you can build in some protection against divide by zero? And multiply the decay value into something a little more user friendly?

[D***@adobeforums.com]

Sure, but you could just set your slider range to something like .01 to 1.0 and then just divide the value by 1000 when you bring it into the expression.

Dan

[M***@adobeforums.com]

Also clamp the input ranges for the slider:

clamp(0.00001,1,effect("Slider")("Slider"))

Mylenium