Car Tail Light illuminations - best way to approach.

[davision]

Note I'm not looking for something perfectly realistic. Just something that looks decent at a distance and is flexibile.

Right now I often create illuminated tail lights/brake lights using standard VrMat. I put a reflector type texture in the diffuse slot and copy to the SI slot. Then I adjust the SI mulitplier to get the look I want.

The problem comes in when I want to re-use this tail light material in a different scene. If it was originally in a night time scene (with a camera at EV 3) then it will have a multiplier of .1 or less, or it will be blown out. However if I use it in a daytime scene (EV 14) it will be incredibly dim unless it has a cranked up SI multiplier of 100 or even more.

It seems to me there should be some consistent value that would work in both situations, since brake lights are visible and day and night and I don't think there intensity changes all that much -- if at all.

I have also tried using the VrayLightMtl for these objects. It has a compensate for exposure option which allows for more consistent values. However this seems like a cheat -- since a light wouldn't really alter its intensity based on camera settings. Is there a "proper" way to set this up.?

[Wilyman]

I guess it depends on the style of lamp, but I tend to hide the bulb/LED geometry and replace it with a VRayLight. Then you can expect cleaner results than a VRayLightMtl (in my experience anyway), and you can set the intensity, colour temp, etc. to the correct values.

I don't think you can expect consistent results if you're emitting light from a reflector object, as that's not the part that would light up in real life, and they're going to be totally different shapes and sizes on different cars.

Cheers,

John

[davision]

The brake lights are not retroreflectors as far as I know. They are light emitters. I don't think most, if any, tail lights have retroreflective properties. It's just light bullbs under normal glass or plastic -- and there is no honeycomb pattern you see on a typical reflector.

I agree a retroreflector is very difficult to set up but I don't think that applies here. Tail lights don't get particularly brighter when you hit them with your headlights. A true reflector would get noticeably brighter (like street signs or reflective tape on the sides/rear of tractor trailers).

When you say you use a Vray light, do you use a standard light or do you convert it to a mesh shape?

I agree that using a Self-Illum material on the plastic shell is not how it works in like real life. But it still seems like the intensity should be relatively consistent between night and day, since I don't think vehicles change their tail light intensity radically based on darkness. I do think they dim a little at night (when headlights are flipped on) but not radically so. Certainly not by the magnitude I have to use in Max when going from day to night anyway. Where it's a factor of almost 1000.

[Wilyman]

Sorry. I don't think my phrasing was particularly clear - I wan't implying that there were retroreflectors involved, just that the mirrored parts of the lamp only light up because they're reflecting a light source. A bulb or an LED.
I inferred from your post (perhaps incorrectly) that you were lighting up the chrome parts themselves, rather than just shining light on to them.

When you say you use a Vray light, do you use a standard light or do you convert it to a mesh shape?

If it's a lamp with a bulb as the light source I'd just stick a spherical light in there instead. It's not exact, but it'll be so overbright in the shot that you won't be able to see the shape of it anyway.

Cheers,

John

[padre.ayuso]

If using VRayLight material, do you turn on the "Compensate Camera Exposure"? This would be a fairly simple approach and it would give you the same light intensity for day and night. Just a thought.

[davision]

Yes, that would probably work. But I want to know when I'm working from a more physical basis (no compensate exposure tricks) that it doesn't work as expected. In real life, tail Lights don't change much in intensity when going from light to dark envrionments (as far as I know) but in Vray the values that must be used to get the proper look between day and night (without camera exposure compensation are absolutely huge). It seems like something related to self-illumination isn't working off of a physical basis.