Car/bike Reflectors -- a semi-realistic model

[davision]

I'm trying to create a car reflector which behaves somewhat realistically (at night).

They work on the principle of total internal reflection (like gemstones) and their reflectance falls off greatly as you move away from a perpindicular.

I have some thoughts as to how to create something potentially decent, but I thought I'd ask the group and see if better ideas surface.

I'm unsure whether to just 'fake it' with falloff maps, or try for the big time and use displacement (or modeling) to get a more accurate effect of light bouncing around.

[joconnell]

Model it - it's the best way to get it to work - you need all the inner reflections to make it look good.

[vance3d]

I think you might take a big rendering hit if you model it to be physically accurate. You might try a parallel/perpendicular fall off material first just to see if the results get you where you want to go. It would be fast to set up and by controling the falloff parameters you should be able to recreate the look you want.

also you might be able to create a pyramid shape and render it as a tileable normal map to use as a normal/bump. I think you would get sufficient reflections from something like that.

V Miller

[joconnell]

You only get the correct look in the reflections if the details are there. I've done a few in the past and having the actual geometry always gave by far the best result.

[davision]

Hey Joe --

I tried a super simple test, and I'm having a hell of a time with the settings.

So far, the best looking effect used a strong non-fresnel reflection with a .6 glossiness since it looked very bright when a beam was shining on it.

However, it seems like a physically correct material would have a fresnel reflections and some glossy refraction... and I'm not even sure if I wanna deal with translucency -- although it seems like that would be in there too. However my tests with these types of settings have resulted in very flat dead-looking materials.

Do you have any tips you could share?

[instinct]

well i can only say that a real model all the way WILL look better. important are also the maximum number of reflections. As in reflectors you got a SHITLOAD of internal reflections. with too few reflections you will end up in black spots. You can tweak those up using the exit color tho.

Regards,
Thorsten

[joconnell]

I normally went with a chrome material - no fresnel on it at all since metals don't obey the fresnel law, and then used fog on the glass that covered the light (it was a red and green light I used last time). Then I plonked a vray area light roughly the size of the bulb in its proper place and hey presto.

[davision]

Oh -- I see what you're talking about. You're describing something akin to a "colored" headlight or headlamp.

I'm talking about something different.


I'm speaking of the reflector only -- no light source. The reflector picks up and reflects incoming light only (like on the rear of a bike). There is no metal in these reflectors that I'm aware of. They are entirely made of little plastic cubes or hexagons which reflect and refract. I'm not certain but I think even brake lights on cars have the same type of reflective covering on the lens so they pick up incoming headlights even if the brake light isn't actually illuminated from within.