Ghost lights and reflections?

L'Adair

magog_a4eb71ab said:

L'Adair said:

handel_035c4ce6 said:

marble said:

I think this is about the lack of speculatity when using Ghost Lights. I normally use a spotlight as well as emissive lights if I want to show shiny surfaces.

What you mean under "emissive lights"? Isn't every surface which has "emission" enabled a ghost light?

Also does the other lights which have "dimensions" work like the glost lights (not reflective)?

In Iray, "Mesh lights" are objects, or parts of objects, that have Emissive properties. "Ghost Lights" are mesh lights with the opacity turned really low, while still having some opacity. (Cutout Opacity: 0.0000001, for example.)

The reason for using Ghost Lights is to brighten a scene without adding a "hot spot" like you'd get with a spot light.

Your eyes adjust to the light in any given space. Pupils dilate to let in more light or shrink to restrict the light. If you walk into a typical bar, for example, after being outside on a sunny day, the room appears to be very dark, with a few bright spots where lights are. But once your eyes adjust to the dim light, the room seems to be lighter, and most of the details become visible.

If you light a similar bar scene in Daz Studio using real light values, chances are your render is going to be really dark with a few bright spots where the lights are. Using a ghost light in such a scene will brighten the overall scene much the same way your pupils dilating will allow you to see better in a dim light enviroment.

This helps in two ways. 1) Iray takes a lot longer to render dark scenes, so the added light will improve the render time and 2) The scene will look much more realistic as all the specular and reflections will all be off the real lights in the scene.

I hope this helps.

The problem I've found with ghost lighting is they can in some cases still appear in reflections, especially on mirror-type surfaces. Also, when you lower the opacity of an emissive surface, it's usually necessary to increase the lumens in order to get the same amount of light output.

The problem the OP was having had to do with opaque Mesh Lights. He just thought they were the same as Ghost Lights.

However, Ghost Lights are just one tool in my tool box. I use them a lot, but not exclusively. I'm not sure why a higher luminance is a problem. Does it adversely affect the render speed? (My own experience would suggest no, but I haven't actually tested by replacing GLs with spotlights.) Or is there some other issue to be aware of?