Translucent Material Ignoring Geometry?

[lectrin]

Hi all,

I'm trying to light up various size glass globes with the same light source. In real life, they use a 1.2W LED which puts out a reported 100 lumen. In real life they are all roughly equally lit.

In keyshot however, the smaller ones seem to light up significantly more than the large. These are made with a translucent material with 8" of translucency. The globes range between 3-5" diameter.

My theory is that keyshot is ignoring the fact that they are hollow and calculating the amount of light that should be transmitted assuming that it's a solid material, when in reality they all have an equal wall thickness of about 1/8". Does this seem like it could be what's happening? Is there any way to avoid this aside from making lights of different brightness in each globe?

Image attached to demonstrate the issue - the samples are low but increasing the samples does not seem to help. Thanks for the help!

[theAVator]

I'm not an expert, but I feel what it is doing is correct. Now, whether or not it should do it this drastically with only a 2" difference in diameter, is another story. But it's not just a brightness and material thickness thing, there is a distance component that is part of it.  Coming from the sign industry, it takes way more LED strips to light a 10'x20' sign cabinet than it does a 4'x8' cabinet. There's something with distance, falloff and spread that all get put into the calculation. You're also drastically increasing the amount of material area that the same light source illuminates - just the surface area change from the 3" to the 5" is almost triple (113.1 versus 314.16). More mathematical minds than my own could figure out the actual volume given the thickness of the globe (I'm no mathlete). In any case, you should expect some dimming from the same light source as the diameter of the globe increases. Maybe someone else can better input on the real world values versus the calculated ones in Keyshot. My suspicion is that if you took a camera and captured an image of the real-world items in such a way as to minimize the amount of glow that it would look more similar to what Keyshot is showing. If you want it to look more like what your eyes perceive, then fudge it in keyshot and eyeball the results till you get the look you're looking for. There may be a more complex way to calculate it, but trial and error might be quicker/easier.

[lectrin]

I agree with your point about the distance, and the surface area calculation does a good job of illustrating the real difference.

I think the 2" distance difference is really what I'm hung up on. I mean a 2" diameter difference is really only a 1" distance difference, and I can't imagine such a small difference making such an impact but maybe it does.

The way they are lit in real life however they are very close in illumination, you really have to look for it to even see a difference.

[theAVator]

Since it piqued my interest, I did some rando googling. I think this sorta describes better what was going through my head, but in 3D space.
https://www.youtube.com/watch?v=LgRiEFGO6v8
My guess is that keyshot is calculating based on this principle??