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Using A DS Distant Light For The Sun In Iray ?

3dcheapskate3dcheapskate Posts: 2,728
edited December 2015 in Daz Studio Discussion

I've just started looking at photometric lights in Iray - I was under the impression from this old post that the 'Intensity' slider was only relevant in 3Delight, and that the Photometric Mode 'Luminous Flux' and 'Temperature' were what controlled the light in Iray. However:

- I set up a simple scene in DS4.8 - one Sphere primitive plus one DS Distant Light

- For the light I set Photometric Mode On, Luminous flux = 98,000* and temperature 5,800 (ballpark figures for sunlight from Wikipedia's sun and sunlight pages).

- I don't change anything else. With the default Intensity setting for the DS distant light at 100% I do an Iray render and it's complete whiteout.

- But if I set the Intensity slider to 0% the lighting looks to be in the right ballpark

So does anybody have a 'good' setting for using a photometric DS Distant Light as the sun ? And more importantly, an explanation for each of the settings ?

 

Note: I specifically do NOT want to use the Iray 'Sun-Sky Only' environment mode, since I have an environment map (LDR - JPG) that I want to use on the Iray dome ('Dome And Scene' environment mode) to provide the GI** component of the lighting.

 

*perpendicular to a surface at sea level, so sort of high noon adrift at sea at the equator on a cloudless day type sunlight, ignoring scattering, etc...

**maybe not the correct terminology, but you know what I mean...

Post edited by 3dcheapskate on

Comments

  • JeffersonAFJeffersonAF Posts: 108

    Hi 3dcheapskate.
    I usually use Photometric Mode for Distant Light with configuration Luminous flux = 15:00 and temperature = 6500.00 and Iray dome.

  • ToborTobor Posts: 2,300

    Leave Intensity at 100, and dial Luminous Flux only. The distant light is measured incident on the scene, not light output from the source. The value is per centimeter square, which is D|S's standard. At noonday sun, the sun drops about 9.3 lumens per square centimeter on the ground. Use that measurement to start.

    Note, though, that Sun/Sky allows for setting haze and other diffusing properties for the light. You will get fairly hard shadows without a diffuser, gobo mesh, or other geometry placed in the direction of the rays from the distant light.

     

  • evilded777evilded777 Posts: 2,482
    Tobor said:

    Leave Intensity at 100, and dial Luminous Flux only. The distant light is measured incident on the scene, not light output from the source. The value is per centimeter square, which is D|S's standard. At noonday sun, the sun drops about 9.3 lumens per square centimeter on the ground. Use that measurement to start.

    Note, though, that Sun/Sky allows for setting haze and other diffusing properties for the light. You will get fairly hard shadows without a diffuser, gobo mesh, or other geometry placed in the direction of the rays from the distant light.

     

    Another post that deserves a thumbs up. We need a way to promote stuff.

  • Oso3DOso3D Posts: 15,084

    Another perspective of potential interest:

    Environmental maps can be set to draw dome off. Why am I bringing this up? Because this still sets lighting and such in the scene... and resolution becomes less important unless you have, oh, mirrors or something in the scene.

    Which meeeeans...

    You could have two backdrops; one backdrop at a low resolution, another at a very high resolution.

    You can use the low resolution in environment map, with draw dome off. This provides the normal lighting and some (fuzzy) reflections where applicable.

    You can THEN hide everything in your scene and replace the environment map to the high resolution map, with draw dome ON, providing a very highly detailed backdrop.

    And then you can composite the first on top of the second and get a coherent, nice final image.

    Why? Well, a really good backdrop can suck up a lot of resources and, I THINK, slow down renders noticeably. I think this approach might save a lot of render time.

     

    You'll note a lot of good HDRI packs come with a much lower resolution 'lighting' map, and I think the above is why.

     

  • 3dcheapskate3dcheapskate Posts: 2,728

    JeffersonAF said:

    Hi 3dcheapskate.
    I usually use Photometric Mode for Distant Light with configuration Luminous flux = 15:00 and temperature = 6500.00 and Iray dome.

    15.00 is rather different from my 98,000 so I guess that's my biggest mistake (and Tobor's response confirmed it). 5,800K v 6,500K - that's the same ballpark

    Tobor said:

    Leave Intensity at 100, and dial Luminous Flux only. The distant light is measured incident on the scene, not light output from the source. The value is per centimeter square, which is D|S's standard. At noonday sun, the sun drops about 9.3 lumens per square centimeter on the ground. Use that measurement to start.

    Note, though, that Sun/Sky allows for setting haze and other diffusing properties for the light. You will get fairly hard shadows without a diffuser, gobo mesh, or other geometry placed in the direction of the rays from the distant light.

     

    Thanks Tobor, that would be it -  lumens/cm² not lumens/m², so I was using a value 10,000 times too big (i.e. 98,000 as opposed to 9.8). So for a distant light only I guess that slider's title should actually be "Illuminance (Lumen/cm²)"  ?

    I've also just confirmed for myself that the "Intensity" and "Luminous Flux (Lumens)" sliders are multiplicative (same as the Iray dome "Environment Intensity" and "Environment Map" sliders) - I had additional dome lighting when I wrote the OP - the following settings all render the same (eyeball test, viewing them side-by-side, environment mode = scene only)
    - Intensity=100% with Luminous Flux=9.8
    - Intensity=10% with Luminous Flux=98
    - Intensity=1% with Luminous Flux=980
    So keeping the distant light's "Intensity" slider at 100% makes sense

    And I do appreciate that there are problems in using a DS distant light for the sun in Iray (e.g. stark shadows, lack of atmospherics, etc) - I'm really just playing with the options at the moment...

     

  • hilguhilgu Posts: 37

    So .... I was curious about these insights here.  I added a DS distant light, Photometric Mode "on", "Dome and Scene" Environment Mode, with an HDRI Environment Map.  Whatever I dialed for the distant light had zero influence on my Iray render.  What am I doing wrong?

  • DrunkMonkeyProductionsDrunkMonkeyProductions Posts: 1,152
    hilgu said:

    So .... I was curious about these insights here.  I added a DS distant light, Photometric Mode "on", "Dome and Scene" Environment Mode, with an HDRI Environment Map.  Whatever I dialed for the distant light had zero influence on my Iray render.  What am I doing wrong?

    The light is too dim.

    Depending on the HDRI you're using, environment settings, and 'tone mapping' settings, you'll probably have to change the lumens upto 25k, or higher, on that distant light to get any visible results.

    In some cases it may be necessary to have it at several hundred thousand to several million lumens.

     

     

     

     

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