Strange Issue with Distant light

carlhungus74

Hello,

After reading lots of tutorials and forums, I'm able to use the DS basics. Posing, Morphing and so on, I can create some cool scenes (according to me of course).

Now I want to light my scene. And my problem is here. I add a figure, a camera, and nothing else. I set Environment to "Scene Only"

When I render with iRay, my scene is correct. I suppose with help of the camera headlamp. If I switch it off, my figure is now  completely black in the render.

Now I add a distant light with default settings. And now my problem : my figure is completely white, like burned by over exposure. 

I think my settings of distant lights are the default one (Intensity 100%, Lumen 1500). If I want to obtain a correct render, I have to set the intensity to 0.30%.

Perhaps I miss something ? but these default values seems strange to me ?

Any help would be appreciated.

 

Sertorial

Yes, I can reproduce this exactly. I never use distant lights, but it does seem that the default settings are WAY too high for iRay. (I guess they were invented back in the 3Delight days) 

I wouldn't bother with the DAZ lights (other than the iRay dome). Create meshlights instead.

SpottedKitty

carlhungus74 said:

I think my settings of distant lights are the default one (Intensity 100%, Lumen 1500). If I want to obtain a correct render, I have to set the intensity to 0.30%.

That actually shouldn't work — Intensity is a parameter for 3Delight lights, if you're working in Iray (Photometric Mode switch should be On) you have to use the Lumen dial.

And don't forget that in Iray lights, you need to juggle the Lumen and Temperature values.

carlhungus74

thanks for you replies. I thought I'm doing something wrong....old habits.... iRay is pretty new to me...but very promising.

 

Sertorial

SpottedKitty said:

carlhungus74 said:

 

That actually shouldn't work — Intensity is a parameter for 3Delight lights, if you're working in Iray (Photometric Mode switch should be On) you have to use the Lumen dial.

 

It does actually work (I did it!). Photometric is on by default and the intenstity dial does actually change the intensity 

The Blurst of Times

I use intensity as well. I usually dial between .3 to .5 , which works with my other settings (especially the camera). I never bother with lumens or temperature on distant light.

evilded777

But why would you use a Distant Light to begin with?

If you are outdoors, Sun and Sky is a much better option.

If you are indoors... um why is there a fake sun indoors? Spotlights and Point lights are your friends, learn to use them! They are much easier to control and provide enormous variety.

 

Not that my opinion is "correct", its just my opinion, after all.

 

Tobor

For Iray, the luminosity of the distant light is measured *incident on the scene*. That means the default 1500 is totally bogus, and is akin to a nuclear blast.

However, Iray is working perfectly, and the math is 100% correct. Here's how to deal with it:

At noon, the sun drops about 9.3 lumens per square centimeter over an earthly surface. Daz's default units of measure is centimeters. So, simply dial the luminosity to about 9 or 10. Leave the Intensity where it is. This is not a parametric setting. Best leave it at 100%.

Someone suggested meshlights. These emit only diffuse light, and follow inverse square law. So while they will provide illumination, it is of a completely different kind than the distant light, which is treated as parallel rays from an infinitely far-away source. In addition to being the opposite of diffuse, another difference is that there is no falloff for distant light, as there is with every other light source in D|S. It does not matter how far the distant light is positioned from your scene. It drops the same lumens per square centimeter at any distance.

 

 

carlhungus74

evilded777 said:

But why would you use a Distant Light to begin with?

If you are outdoors, Sun and Sky is a much better option.

If you are indoors... um why is there a fake sun indoors? Spotlights and Point lights are your friends, learn to use them! They are much easier to control and provide enormous variety.

 

Not that my opinion is "correct", its just my opinion, after all.

 

I used this kind of light some years ago in various 3D software. I think it's time to move on... Will try the sun & sky in DS.

 

Thanks to all for your very useful comments.

Fishtales

I use a Distant Light as it is just the first one that comes to mind :)

I used it as a back light on an interior scene of a space ship cockpit that had no back wall. There was light from the HDRI illuminating the interior but I wanted a bluish light from the back that would make it appear that there was more to the space ship than was in the scene. I also noticed that lowering the Intensity from 100% would soften the shadows thrown by it.

Click on image for full size.

 

Steven-V

1500 Lumen is way too high for distant light.

I have done some (not perfectly controlled) testing using a Distant Light as both sun-sky node or as a light source.  To get the same exposure from the same tone map settings, you need something like 10-15 Lumens on the distant light, not 1500.

I am not sure (I have not tested) whether this depends on just how far away the distant light is. it shouldn't -- only angle should matter with a DL -- but this probably won't change the order of magnitude you need for the # of lumens.

Also, %intensity does work... so you can either set the lumens to 10, or else set intensity to 1% or something. Or a combination.  Personally, I like messing with lumens rather than intensity, but I don't have a really good reason for it.