Is IES light really true?

[Higuchi]

Hi guys,

I'm testing some IES light published on light maker's website for closed space. Let's see a sample "LGD1010V", which is really typical one in Japan, made by Panasonic.
https://www2.panasonic.biz/ls/catalog/lighting/products/detail/shouhin.php?at=category&ct=juutaku_catalog&id=S00160905&hinban=LGD1010V

My question is about how proper IES light is on Keyshot compared to physical world. As far as I know, multiplier "1" is as same as real product. But, "1" looks  so insufficient of light power. When the number is adjusted to about "10", the appearance looks nice. How do I understand the situation?

I guess each CG renderer, Keyshot, V-Ray, Corona, I-Ray, and so on, has different standards for material setting. So, I can understand there are also difference about IES light, but my examples expresses too much difference, doesn't it?

[andy.engelkemier]

I have no idea if keyshot's IES lights are correct. But one thing, when dealing with lighting and material, if you hope to see what something looks like and have it physically accurate, is to watch out for scale. This is something that keyshot has never been great at. In fact, one of it's default settings was to automatically scale your objects to be a "good" size for keyshot to handle.
This actually makes pretty good sense with respects to things like global illumination. But in terms of being physically accurate, it's Just pure evil.

Light is Very scale reliant, especially when it comes to light intensity. If you have a small flashlight and light up a small white box full of miniatures, it'll look like it's real-scale almost right? Well, the same thing in 3d, only you lit that thing with only 100lm rather than 1200 lm.

In Some 3D software, you can change the units, but certain units will always work on it's default scale (I'm looking at blender with a glaring eye here, in relation to physics).

So be sure you've got scale correct first. Check your scene units, and the scale of your objects in keyshot. Scale in keyshot....well, it can be terrible. Try scaling in one direction and see what happens to your scale numbers. It's a bit of a mess.
So do your best to get scale correctly right out the door or prepare for a messed up keyshot experience.
Also, be sure every import you have used the same units Before it comes into keyshot.

[Higuchi]

Thank you so much, Andy,

That is likely the very what I want to discuss! Actually, I'm trying to make new space model as the attached image. As far as I checked it, the model size seems to be correct due to the number 2,400mm height.

Let me confirm what you pointed out, just in case. You advised me how accurate entire model size is, not the model size applied as IES light material is, didn't you?

As far as I know, the model size applied as IES light material is not related to how bright it is, although some other light materials such as Area light controlled with Lux, not Lumen, depend on how big the model is. *reference article below and attached caption
https://manual.keyshot.com/manual/materials/material-types/light-sources/area-light/

[andy.engelkemier]

Be sure also to check the scale of the parent. Each object can be individually scaled. Often when you import you will see a part with a scale of 1.0, but the parent has a scale of 10, or .01. This is what I was looking for, to be sure.

Also, I don't know enough about IES lights to know if you can scale them, but my assumption is that you should leave the scale at 1, otherwise you're adjusting the light definition? I haven't used them since around the time of hypershot, and I used them in 3dsMax. So I may not be of much help, other than pointing you in the scale direction having an effect on the materials and lighting.

[Higuchi]

I understood what you said. I actually didn't have an awareness for parent's scale. But, when I confirmed it, the parent's scale also 1.0. They seem to be accurate regrading as the scale.

I'll repost on this thread, if I can get some other rule for IES light.