Hierarchical light shadow strangeness

[R Reynolds]

I'm building a railroad indicator lamp, essentially a red/green traffic light. I wanted to simulate the look of the optics of these lights which were designed by mounting an incandescent lamp at the focal length of a coloured glass fresnel lens (like in a lighthouse) such that its light is only visible when viewed almost on-axis as one would from a long distance. I think I've come up with a believable result using a hierarchical klieg light mounted inside the enclosure. It's aimed to shine inside the case and illuminate a small internal disc, standing-in for the lamp filament, sitting near the focal length of the lens. Viewing the indicator while it turns in front of you produces a result I'm satisfied with.

The problem is that, as far as I can tell, hierarchical lights (sun, bulb or klieg) do not handle well the shadows of other parts of the model. I set up a test model that's similar to my indicator lamp.

Inside the open sided box is a klieg light aimed at a target disc that in this case has a hole in its centre. In any render from the modeling window there are no shadows generated by any surface regardless of whether the shadows are ray-traced or Z-buffered. Strangely a chor render does have translucent ray-traced shadows but the light still passes through the entire model and falls on an external model.

My work around was to make an inside screen that was totally black so the light hitting the rear of the case is absorbed and only the target disc is illuminated. As for the light leaving the back of the enclosure, I'm fortunate that there will be about 4 ft. (1.2 m) between the rear of my indicator lamps and the nearest surface so I should be able to set a fall-off value that minimizes the spill.

I suppose since hierarchical lights are typically used for things like automobile headlights this has never been an issue before. However you'd quickly notice this glitch  if you were trying to shooting a night scene using the dome light of car as illumination. The passengers would have shadows while the other parts of the car would not.

Obviously the ultimate work-around would be to add the lights in the chor but it would be nice to have this convenient feature work.

[robcat2075]

Rodger, could you post your sample PRJ that demonstrates the problem?

 

The effect in your animation is very convincing!

 

[robcat2075]

Rodger, make sure the Options>Cast Shadows>Darkness of your light is set to 100%.

 

Although new lights default to 80%, 100%is the more typically useful setting.

[R Reynolds]

Right you are sir!

Once again you've shown me the light. 😄

Thanks Robert.

[R Reynolds]

Another issue with hierarchical lights is that once you add one to the model, they become the light source for real time screen renders. This is especially annoying when the light source is inside the model. Is there an option that keeps real-time screen renders using the default light source that's at the camera?

[robcat2075]

This seems like a shortcoming.

There is "Use Front Realtime Light" in the Chor but nothing like that for the Modeler or any other window.

Quote

If this is ON, then all of the lights in your scene are ignored. The scene is lit by a bright front view light like the one used in the model window. This is useful when a scene has more lights than are handled by the video card.

 

Perhaps this could be extended to the modeler as a general parameter in the Options window. If it had a button,what would the button look like?

[R Reynolds]

Here's my first guess for camera light icon at 4X full size.

[robcat2075]

I was imagining something like a doctor with the mirror on his forehead but yours looks like the existing camera icon
 

http://www.politedissent.com/images/jun10/camels.jpg

 

[R Reynolds]

Hey, I paint what I see and steal what is useable.