Ghost Lights Kit vs Spotlights or Emissive Objects
Joe827
Posts: 236
Hi folks. I am looking at https://www.daz3d.com/iray-ghost-light-kit, and would like to understand in what ways you all are using them. In the promo materials, I see ghost lights placed in front of windows and on light bulbs. My initial thought is that you could achieve the same thing with a wide angle spotlight in front of the window and to set the bulbs to emissive in the surfaces tab. In other words, what need do the Ghost lights fill that can't be accomplished using Daz's native lights? I am likely missing something obvious that will 'click' the moment I post this. 
At the very least, it looks like the window ghost light would be easier to use than the spotlight.
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Comments
The ghost lights are so versatile, once you start using them, (in Iray,) you'll wonder how you got on without them.
Because they are "ghosts," you can add light without getting any reflections. Existing light goes through them and they don't cast shadows. Take my last render:
I'm using a distant light for the moon but it left really harsh lines between the lighted and unlighted areas of the figures, especially on the reindeer. The shadows were much darker as well. I'm using emissives on the windows to get that lighted house glow, but I also added one ghost light in front of each window and the glass on the door, set the temperature to a light blue, (7000, I believe), And used that to brighten the backsides of the figures. There's also a small ghost light in front of Santa's face to brighten the stark shadows there.
In a real life situation, the reflection of the moonlight on the snow would brighten up the image considerably, but that's not happening in Iray. By adding the ghost lights, I was able to simulate that effect in just a few minutes. Ghost Lights are both simple and powerful. They create the best ambient light in an Iray scene, IMHO.
Here's a short tutorial on how to make your own ghost lights, shared by the vendor who produced the ghost light kits, I personally have found the products to be time-savers, but if you want to test this out for yourself first, follow the steps in the tutorial. I think you'll be glad you did. Even if you choose to DIY rather than picking up the kits.
A wide angled spot light is nothing like a ghost light near a window. A ghost light will be sized to cover the windows, which means light coming in over a large area. A spot light would give light from just one point, so would give far harsher shadows inside the room. You can give the spot light size, by changing the type to sphere, but then a white sphere will appear on the render if the window is in the render view.
Ah ha. That's the piece I was missing. Makes sense now.
The biggest reason to buy the ghost light kit is the ease of use. I use it to fill in dark spots in a render all the time, its one of my most used products. Can't say enough good things about it. Yes,I could do it myself. But I don't want to. And I don't really have time,
Thanks for your feedback. That is good to know.
I generally use the Iray Ghost Light Kit to light the characters in a scene that is otherwise lit. For example, if I am doing an ourdoor scene and the sun is high in the sky, the character(s) faces can have shadows due to the angle of the light vs the camera. The ghost light helps eliminate that.
I also use them when I either can't use 3-point lighting or don't want to spend the time.
They are a quick solution that works well, and they are a tool I recommend.
Edited to add: I don't use them to replace emissive objects, like a lightbulb, but they allow me to light the scene without relying on the lamp. That way, I can have the lamp bulb's emission set to on, to add a touch of realism, but it is not as bright as the sun, which would ruin the effect.