Several questions about Ghost lights

handel_035c4ce6

As recently I started to experiment more and more with the gjost lights I would like to understand few tech details about them.
So:
1. Does 2 sq m ghost light gives 2 times more light exposure then 1 sq m ghost light with the same lumens?

2. When the ghost light is 2 sided and it is set to (for example) 100.000 lumens, does each side gives away those 100.000 lumesn or it is 2x50.000?

3. I think I've seen an option to make (light) portals but cannot find the option now; please advise

4. Does the ghost light which is set to not be rendered still gives the same light?

5. Does a ghost light which is turned invisible still gives the same light?

6. The same question if the ghost light plane is made 100% transparent?

7. I ask the last questions because I made experiments and it seems I saw some slight "mist" in the render when the ghost light was turned invisible or was set not to be rendered. Is there any other way to make the ghost light invisible in the render but still giving away the desired light?

Richard Haseltine

1. No, if you set an absolute illumination value (rather than using the per m^2 option) then making the light bigger just spreads the same amount of light out more.

3. Light Portals are, or were, an option with spot lights - using them to channel light from the HDR. I'm not sure theya re still supported, since soem of the features associated with them have at least been deprecated if not removed.

4. Yes, though it makes very little difference.

5. No, it's off

6. Transaprency must be non-zerp for Ghost Light to work.

handel_035c4ce6

Richard Haseltine said:

 

4. Yes, though it makes very little difference.

So I can put a ghost light in a camera frame field and set it not to be rendered; therefore it will give the desired light but will not interfere with the final render, right?

 

Richard Haseltine

The whole point of a gjost light is that it has a very low, but non-zero, opacity.

On portals theya re still there, even in the beta. Create a Spotlight, set its shape to Rectangle, and a button for Portal will then appear and can be switched on - though as I say, they are supposedly of use only in very limited circumstances and not - I would expect - in conjunction with ghost lights.

L'Adair

handel_035c4ce6 said:

Richard Haseltine said:

4. Yes, though it makes very little difference.

So I can put a ghost light in a camera frame field and set it not to be rendered; therefore it will give the desired light but will not interfere with the final render, right?

I've never had a Ghost Light interfere with the final render, regardless of where I put it. Are you using KA's Ghost Lights, or making your own? If you're making your own, and the mesh is somewhat visible in your renders, try setting the opacity to something really low, like 0.0000001.

If you want to limit the light to a spotlight, you can plug a mask, (black and white, like an opacity map,) into the image slot of the Emissive Color setting. I've only used circles, both hard edged and blurred edge, but I suppose you could try getting creative. Also, if you set Cutout Opacity to 1, you'll get specular highlights. I've not tried it, but it sounds like you could make the light opaque and then set Visible In Render to Off. And if you don't want to see it in your viewport, 4.11 has a Visible in Viewport setting as well. (Not sure if 4.10 does as I skipped that version. I can verify it is not available in 4.9.)

I don't know the technical aspects of a two sided light, but I've never noticed a difference in lighting the area in front of a Ghost Light when I've set it to two-sided.

I hope this helps.