Spotlights, Ghostlights, and Sun-Sky Only

MeneerWolfman

I've run into this issue from time to time and figured I would finally ask for advice.

In general, I use ghost lights for lighting scenes after the main hdri or emissive objects in the scene.

However, ghost lights won't cause an object it hits to create a shadow. E.g., put a ghost light outside of a window pointing into the room, the ghost light's light will go through the window glass and into the room, however no shadow from the window's frame will go across the floor.

If I use a spot light instead of a ghost light, I will get the shadow across the floor effect.

Question A.) Why is that? And anyway to do the same with a ghost light?

Question B.) I'm okay with it being something that only a spotlight can do, however, my second issue comes in that if I use sun-sky only rendering mode, no spotlights show up  Is there a way to get spotlights to appear in sun-sky only mode?

 

Thank you.

TimberWolf

A) - Ghost lights will create a shadow. I suspect your ghost light is large compared to the geometry of the window frame and this will limit the effect quite considerably, softening the shadows perhaps to the point of non-existence. Point lights or directional lights produce a far more focused beam and will show the effect more noticeably. Try shrinking your ghost light and see if that helps.

However, I expect that your other question will mean you don't need to bother with ghost lighting.

B) - Sun-Sky Only really means exactly that. Only sun... only sky. No other lights except emissive materials will work. To get round this change the Environment Mode to Dome and Scene, set the HDRI map to None and you have exactly the same ambient lighting but now scene lighting will work. You have exactly the same parameters as Sun-Sky Only to work with as well.

I hope this is what you were after but I'm not entirely sure I've got to the root of what you want...

MeneerWolfman

Hi TimberWolf,

Thank you for the reply.

To point A, are you suggesting that if I shrink the size of the ghost light primitive down it will focus the beam (for lack of a better term) to something that will generate the same shadow effect as a spotlight?

 

To point B, isn't that just the same as scene only? I'm not sure what I'm getting with that path. My interest in sun-sky is because of the background it will generate and accurate lighting for twilight and dusk scenes where it's not pitch black outside. Usually in a pinch, I just throw a plane primitive behind the window with a small emissive from said plane and a prerendered background to fake it. Ideally I would like to have sun-sky, but still get the dramatic lighting one gets with a spotlight.

TimberWolf

A) - Yup. Shadows get softer the larger the light source is compared to the subject (in your case a window frame's geometry) and if your ghost light is particularly big it  willl effectively cancel out any shadowing. Great for female portraits but not really useful for what you want. However, I'd stop messing with ghost lights because:

B) - No! Dome and Scene with no HDRI map will product the *exact* same effect as Sun-Sky Only, with the same parameters - time of day, lat/long etc. However, your spotlights, point lights and directional lights will work. Try it.

MeneerWolfman

Oh wow, I would have never have assumed that and have never tried it since that default hdri image always populates

I'm really glad I asked 

Thank you so much for the tip, that was exactly what I was looking for :)

TimberWolf

It's not intuitive, that's for sure! Logically, you would expect Dome and Scene with no HDRI to produce the same lighting effect as Scene only, exactly as you suggested, but... it doesn't.

Sun-Sky Only is a pretty redundant rendering mode in my opinion but perhaps there is some subtle difference between that and Dome/Scene with no map that I'm unaware of. Glad I could help you out.

Richard Haseltine

TimberWolf said:

It's not intuitive, that's for sure! Logically, you would expect Dome and Scene with no HDRI to produce the same lighting effect as Scene only, exactly as you suggested, but... it doesn't.

Sun-Sky Only is a pretty redundant rendering mode in my opinion but perhaps there is some subtle difference between that and Dome/Scene with no map that I'm unaware of. Glad I could help you out.

Why would removing the HDR swuitch the doem off (to be the same as Scene Only)? I can see it is a possible behaviour, but since it does duplicate Scene Only I am not sure how useful it would be. Having the HDR replaced with Sun/Sky keeps the Dome part relevant, and allows for easy comparison. Sun Sky and Scene Only are still both useful for limiting the effect applied without removing other things.