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Question Using HDRP for simulating real lights and getting luminance values

Discussion in 'High Definition Render Pipeline' started by Rylern, Sep 30, 2022.

  1. Rylern

    Rylern

    Joined:
    Jan 24, 2020
    Posts:
    6
    Hi,

    I am currently working on a research project that aims at simulating real lights using Unity with HDRP. The goal is to have features similar to Dialux, mainly getting luminance values on a pre-defined plane.

    My first goal is to create the same simple scene in both Unity and Dialux, and compare the light intensity displayed by the two software:
    • In Dialux, I defined a 10x10 meter white ground and placed the 99 527 K3 light 3 meters above the ground.
    • In Unity, I defined a 10x10 meter white plane and placed a point light 3 meter above the plane. I set the IES file of the 99 527 K3 light on the point light, and defined the correct intensity in Lumen.

    However, here is a top view of the two scenes:
    • In Dialux:

    • In Unity:

    You can see that the shape of the lighted surface is quite similar for both Unity and Dialux. However, the area covered by the light is way larger in Dialux.

    Do you know why there is such difference? Since it's a lighting software, I tend to think Dialux is closer to reality than Unity.

    Thanks in advance for your consideration!
     
    soleron likes this.
  2. Remy_Unity

    Remy_Unity

    Unity Technologies

    Joined:
    Oct 3, 2017
    Posts:
    703
    I wanted to double check but was not able to properly import the IES profile from the page you've linked. Did you somehow pre-process it ?
    On my side it generates light cookie texture that don't look at all like what you've shown : upload_2022-9-30_19-13-41.png
     
  3. Rylern

    Rylern

    Joined:
    Jan 24, 2020
    Posts:
    6
    Thanks for the quick reply. Indeed, I forgot to mention that I use the Photorealistic lights (IES) asset to import the IES file. I don't use the IES importer of Unity because I will need to import these IES files dynamically (not only in the editor).

    But actually even when I use the IES importer of the Unity editor I have the same problem: the covered area is smaller than what I get with Dialux. Here is a screenshot (same light, IES importer of Unity, light rotated of 90 degrees on the x-axis and 180 degrees on the z-axis to get a similar shape):
     

    Attached Files:

  4. Remy_Unity

    Remy_Unity

    Unity Technologies

    Joined:
    Oct 3, 2017
    Posts:
    703
    I've tried with the mentioned asset, and managed to have a similar result :
    upload_2022-10-6_12-29-21.png

    I simply had to set the spotlight angle to 170°, as the generated file itself mentions it:
    upload_2022-10-6_12-30-27.png

    Now, I don't fully understand why the HDRP built-in IES importer doesn't give the same result ...

    Hope my finding will fix your issue.
     

    Attached Files:

  5. Rylern

    Rylern

    Joined:
    Jan 24, 2020
    Posts:
    6
    Thank you, I realized what I did wrong. I created a plane and changed its scale to (10, 0.1, 10), thinking I was representing a square of 10 meters per 10 meters. However, the scale doesn't represent the length, so I was working with a too wide plane. This is why the covered area was so different.
    Anyway, thanks for the help!
     
    soleron likes this.