how do i make eyes glow like a cats eyes when shined a light on them?
do you know how to use the compositor?
Some what, I under how it works, Just donāt know how to get the effect exact.
The effect is like a greenish with a lil yellow in it. And looks reflective like a sign is when light reflects off it at night.
tutorial will help understand: http://www.blenderguru.com/videos/introduction-to-the-compositor
Hereās another thought ā¦
āWhat makes a catās eyes glow?ā Well, they glow when the light shines directly at them. But, in CG terms, what does that mean? It refers to the relative angle between the light-source and ā¦ careful now ā¦ some (invisible?) plane within the eye which corresponds to the retina.
(You might āfakeā the actual effect by causing a shape corresponding to the pupil-opening to generate the actual āglowā response. There are several ways as-shown to generate the glow.)
The orientation of a plane is expressed by its surface normal, which you can get as a compositing node-type. The normal is a vector that points directly āoutā from the plane, directly ātoward the āfront.āā And what you are looking for is a function of the differences between that vector and the vector of the camera.
(Ignore this paragraphā¦ see next paragraph.) You can get āthe basic illumination of the fake-retina planeā by putting it into some group and defining a group-only light at the position of the lights-of-interest which will āshine directly uponā that retina plane without regard to any troublesome enclosing-objects, such as the eye. You donāt plan to use those illumination values except as inputs. (In fact, you need to take steps to ensure that the light that shines on that retina doesnāt get figured into the actual image output, except as specified by your node network. You donāt want to see that plane, but you do want Blender to figure out how much light is shining upon it by ā¦ either the various interesting lights, or, as I suggested, special-for-this-purpose ālightsā at the same locations in 3D space.
Or maybe you just decide to simplify, and ignore the entire preceding paragraph on the assumption (probably true) that it wonāt make any difference. (If a difference wonāt make any obviously-visible difference in the final output, donāt implement it.) A catās eyes gather and concentrate light from any direction ā¦ and spooky-catās eyes glow in the dark even in complete darkness. So, the only math that you have to consider is the angle between the surface-normal and the camera.
One cheap-trick that is sometimes handy in math like this is to define an empty, parented to the retina-plane, which always points (via a constraint) directly at the camera. This gives you an easy vector to compare to that of the retina-plane because itās pointing the same way.
This usually winds up as āa little subroutine, or macroā in your node-network (borrowing the computer programming term), which is set up as a āgroup,ā so that you can define it once and use it in many places. It basically calculates, as its output, the desired intensity of the glow (in the range 0.0 ā¦ 1.0, say), and you use this to modify the intensity of the glow-effect on the desired object.
The sphere of a catās eye will of course reflect some amount of light because, like all eyes, it is wet. But when it starts glowing at you, well, thatās the time to get out that second little can of cat-food. 
(Or at least, thatās what my cat is always rubbing against my leg, trying to convince me, usually with success.)
Dude, You are amazing. But infact Im not using it for a cat, itās for a paranormal activity movie. But another resource of mine said this and I quote āIf you want it to respond only when light is directly on it, give the pupil a mirror, and Wardiso spec, with 0.0001 for the hardness and 1.0 for intensityā And Iām sorry if you said this in your awesome paragraph. Which by the way was very helpfull in deed. But would this give me a good effect? Cause I have noticed that there is like two types of color in the eye when light hits it from and angle. So I want to combine this and a kind of glare effect. So can you tell me about the glare effect? Like a sun flare or whatever it is.
I really havenāt encountered the trick that your friend is referring to, so I quite honestly cannot comment on it at all.
Being a computer programmer by trade, I find myself thinking like one ā¦ which basically means breaking down any problem into its component parts and figuring out some way to program a digital computer to do the right thing ā¦ whatever āthe right thingā might happen to be. Therefore, when you tell me āthere are two types of color in the eye when the light hits it at an angle,ā my response is exactly as before: I want to turn it into an if-statement. 
āThe final image that you see,ā from the point-of-view of the computer, is, more or less, āthe output of a computer program.ā And by āa computer program,ā in this case I really donāt mean āBlender, itself,ā but rather, the output of the instructions that you gave to Blender in the form of various node-networks. (It could be more complicated yet than that ā¦ if youāre compositing, then āthe final imageā is the product of combining two or more intermediate results, each one of which was produced in some similar way, ad infinitum.)
Neverthelessā¦ the way that I try to think of it (and, mind you, who-the-hell says that what I am doing is right, or that my crazy ways should be imitated by any other fool?) is: to break down the problem into its individual components (e.g. ā(1) the color when the light isnāt hitting it, and (2) the color when it isā), and then to devise a rule for the computer to blend the components together, based on some set of parameters (e.g. angle of some plane vs. angle of camera) that I figure that I can actually get my hands on. I also want the final result to be adjustable, as many times as I may care to adjust it, without re-rendering.
For me, it is very definitely a matter of successive refinement. I never try to get everything to come together āin one grand-poohbah render.ā Quite the opposite. There might be dozens of digital pieces all scattered about on the floor of my hard-drive waiting for some final composite to bring them all together. If your friend made his observation and I decided that it really would make a human-noticeable difference in the final result, I would consider how I could incorporate that finding into the final-output while re-rendering as little (if anything) as possible.
Iād try to say: āokay, this is great, and I am totally satisfied with it now except for my friendās suggestion. Therefore, how can I incorporate my friendās suggestion into this workflow while re-rendering little, or better yet, nothing at all? Furthermore, if I decide to discard my friendās suggestion, how can I get right back to where I am now without having to re-do anything?ā Iād like to get a ābeforeā picture and an āafterā picture so that I can easily and painlessly decide whether to keep it or to dump it.
I found quick and easy workaround for this. Set your Iris to be a hole with glass material (like a lens - see proper eye anatomy), then make inside of your eye an emission driven by layer weight. Now every time your character looks at camera itās iris will glow in a believable way. Hope this helps somebody. Cheers
this is hot stuff, still incredibly useful
You can simulate this using volumetric scatter
Ok, a little update. I found a way to simulate it realisticly so it acts like a real world cat eye. All you have to do is change emission material of eyeās inside to retroreflective material. That way, everytime an eye looks directly at light source it will glow.
Very simple retroreflective material.
Mirror inside of an eye
Have fun.
Hello there,
I know it is a pretty old post, but IĀ“m wondering if you could share the files used to create those results.
Several months ago I tried to create realistic red-eye artifatcs in simulated human eyes using cycles and real-life lens specs but failed!
Really good results, by the way!
Hello there.
Somebody already made a tutorial for this
However, instead of making the iris retroreflective make it in the bottom of the eye. For that to take effect the pupil must be a hole. Then light goes through pupil and retroreflects from the bottom of the eye and gets back to camera. For eye I always go with this tutorial:
Happy blending!
Owhhh. Really thanks for the reply. IĀ“ll try!
There is another way that reacts to Light, like a flashlight or headlightā¦
and as about as simple as you can getā¦
Owwww. IĀ“ll try both solutions.
Thank you very much for sharing!