Ghost Lights: Interior lighting Tutorial

KindredArtsKindredArts Posts: 1,041
edited January 2017 in The Commons

Hello. I know some of you are highly proficient when it comes to the technical aspects of lighting, and some of you render on very powerful hardware. Just a warning, this probably isnt for you! If however, you are rendering on lower end hardware, or are finding it hard to render interiors without lots of grain, this IS for you! 

Window lit rooms are a tricky beast due to the fundamentals of pathtracing. It relies on a lot of GI bouncing through refractive glass, which is a computational nightmare. You could start tearing down walls, hiding meshlights out of shot, use light portals or even hidden photometrics. All of these methods have pros and cons, but the best solution i've come across are ghost lights.

Ghost lights are invisible mesh lights that can be placed near a source of light to boost the amount of light being emitted directly into the scene. They are invisible, they do not effect reflections, and since they can be done with single poly planes, they are incredibly cheap to render.

Here is a before and after, using a single Titan x (This is useful for much lower end hardware). This is a completely enclosed room, no cheating!

Here's how it's done....

Create a new plane by going to create - New primitive - plane. Now place this plane over the windows, or above a ceiling light, like so:

Once you've placed all your meshes, you need to go into the surfaces tab and apply the Iray uber shader to the planes material zone (The uber shader is in your shader folder). Now change the following values:

Do not play around with anything other than the Luminance and emission temperature unless you know what you are doing. You can however set "Two Sided Light" to *off*, but you must make sure the plane is aiming in the right direction before hand.

I'm going to keep this short and sweet because i'm disastrously busy today. Please let me know if this helps any of you, and if you find it hard to follow, let me know so i can update this tutorial. I'll try and update it soon with some other tricks and cheats you can take advantage of. Until then, happy rendering!

Noghost.jpg
1920 x 1080 - 2M
Position.jpg
1916 x 1040 - 813K
Settings.jpg
1913 x 1036 - 693K
Withghost.jpg
1920 x 1080 - 2M
Post edited by KindredArts on

Comments

  • Serene NightSerene Night Posts: 13,610

    very cool tutorial. Thanks for the tip. 

  • KindredArtsKindredArts Posts: 1,041

    very cool tutorial. Thanks for the tip. 

    You're very welcome!

  • I knew how to do this, but usually don't remember to do it.  I had no idea, though, that it made such a dramatic difference.  Those two renders were real eye openers.  Thank you for sharing this.  I think I'm going to have to rethink using this technique a little more often.  :)

  • KindredArtsKindredArts Posts: 1,041

    I knew how to do this, but usually don't remember to do it.  I had no idea, though, that it made such a dramatic difference.  Those two renders were real eye openers.  Thank you for sharing this.  I think I'm going to have to rethink using this technique a little more often.  :)

    Glad to help KM! :)

  • barbultbarbult Posts: 11,021

    Very interesting. Is there a reason for setting the emissive panes to two sided?

  • Joe WebbJoe Webb Posts: 777

    Wow, nice, thanks for the great idea.

  • KindredArtsKindredArts Posts: 1,041
    barbult said:

    Very interesting. Is there a reason for setting the emissive panes to two sided?

    Nope, one sided is fine. This was aimed at beginners though, and i had a horrible feeling that they might place them the wrong way round and then shout at me because nothing was happening.

  • mjc1016mjc1016 Posts: 15,001
    barbult said:

    Very interesting. Is there a reason for setting the emissive panes to two sided?

    Nope, one sided is fine. This was aimed at beginners though, and i had a horrible feeling that they might place them the wrong way round and then shout at me because nothing was happening.

    I was going to mention something about that yesterday, then realized there's a lot less playing around with it if you don't have figure out which side the light is coming from.

    If the plane is pointing the right way, it's a simple matter to just flip Two Sided to OFF.  That may shave a couple more seconds/per light off the render time.

  • KindredArtsKindredArts Posts: 1,041
    mjc1016 said:
    barbult said:

    Very interesting. Is there a reason for setting the emissive panes to two sided?

    Nope, one sided is fine. This was aimed at beginners though, and i had a horrible feeling that they might place them the wrong way round and then shout at me because nothing was happening.

    I was going to mention something about that yesterday, then realized there's a lot less playing around with it if you don't have figure out which side the light is coming from.

    If the plane is pointing the right way, it's a simple matter to just flip Two Sided to OFF.  That may shave a couple more seconds/per light off the render time

    Mjc, i was wondering when you were going to pop up and tell me why i'm completely wrong, but you didnt, so good times! I'll update the tutorial later with a note about two sided lights. 

  • PedroCPedroC Posts: 125

    yes

  • IceDragonArtIceDragonArt Posts: 12,073
    barbult said:

    Very interesting. Is there a reason for setting the emissive panes to two sided?

    Nope, one sided is fine. This was aimed at beginners though, and i had a horrible feeling that they might place them the wrong way round and then shout at me because nothing was happening.

    I would so do this.  Not shout at you but turn it round and wonder what the heck I was doing wrong lol.

  • Sweet! Thanks for the tutorial. Much appreciated. laugh

  • mjc1016mjc1016 Posts: 15,001
    mjc1016 said:
    barbult said:

    Very interesting. Is there a reason for setting the emissive panes to two sided?

    Nope, one sided is fine. This was aimed at beginners though, and i had a horrible feeling that they might place them the wrong way round and then shout at me because nothing was happening.

    I was going to mention something about that yesterday, then realized there's a lot less playing around with it if you don't have figure out which side the light is coming from.

    If the plane is pointing the right way, it's a simple matter to just flip Two Sided to OFF.  That may shave a couple more seconds/per light off the render time

    Mjc, i was wondering when you were going to pop up and tell me why i'm completely wrong, but you didnt, so good times! I'll update the tutorial later with a note about two sided lights. 

    Nah...nothing wrong with this technique.   Even leaving two sided on makes sense, in this case.

    It will work in 3Delight, too.

  • mjc1016 said:

    It will work in 3Delight, too.

    For clarity sake, which one do you add for 3Delight?  UberAreaLightbase?

    Looking in the Files/Lights/other I see items like Light Plane, Light Sphere, Light Tube, UberAreaLightDisk, UberAreaLightPlane etc.  Would any of those be applicable for situations like this?  I rearely hear anyone mention those.

  • mjc1016mjc1016 Posts: 15,001
    Stryder87 said:
    mjc1016 said:

    It will work in 3Delight, too.

    For clarity sake, which one do you add for 3Delight?  UberAreaLightbase?

    Looking in the Files/Lights/other I see items like Light Plane, Light Sphere, Light Tube, UberAreaLightDisk, UberAreaLightPlane etc.  Would any of those be applicable for situations like this?  I rearely hear anyone mention those.

    Yes, UberAreaBase applied to a plane.  Or the Light Plane will also work...

    Here is one with UberAreaLight Base applied to a plane, sized and placed over the window of the door.  Opacity is set to 0.001%. 

     

    3dlghostliight.png
    640 x 512 - 630K
  • nowefgnowefg Posts: 441
    edited January 2017

    Just a quick note: I'm using 4.9 on a 2007 Lenovo T61, Core2-Duo, Invidia 140m onboard "graphics", and 2 gb accesible ram, with an SSD system drive and an outboard HDD data drive. I finally found a way to do a non-crashing Iray render, by setting a system-managed paging file on my outboard USB 2 HDD. The paging file has to go on the outboard, because paging is contraindicated for SSD's, so it does have to squeeze through that USB 2 bottleneck.

    This, I think, qualifies as "lower end hardware."

    I have struggled to get predictable interior light in a scene like KA is showing above, and have been wishing for an Iray option something like AoA's Ambient lighting, which I use in most 3DL renders. I've purchased a couple of Iray interior lighting sets, but they seem more suited to portraiture, and do great job at that, but I want the lighting freedom I'm used to in 3DL.

    I took KA's Ghost light tip, here, and was shocked at how well it works, and what subtle effects are possible, especially by using different colors on several ghost lights, like a blue coming in the windows on the shadow side of the room, and a golden light coming from sun-side windows. To do that deliberately, without trying to guess at what a given HDR is going to come up with and rotating ad nauseum, is a tremendous restoration of my artistic exhiliration. Just huge fun.

    The renders still take "a bit" more than 2 minutes, but what I get for waiting is so much richer and more fun than trying yet-another HDR and hoping it looks "kinda" like I "wish" it would. A couple of hours of experimenting with ghost lighting showed me I can do whatever and exactly what I want, even given the hardware constraints. Struggling about which side emits, I found that using a glaring color and blasting the luminence makes that easy to find out, and then rotate the primitive and switch to more nuanced colors and luminence. Experimenting with that "which side" process was such a trip, because it showed me I can do anything, exactly as I want to, and still have a lot of room for physically-based-light magics to happen in the mixing and bouncing of light interactions and reflective surfaces.

    So far, a simple-scene fifteen minute render is still quite grainy, and a one hour render needs more time, but a five minute tweak render shows enough to see how the lights are working and where the render is going, and stop to adjust ghost light angles and colors. To be realistic, I don't know how long it would take to get a smooth looking render like I see above, probably a few hours, if even then, but I do have confidence now that however long it takes, it will be the render I wanted. So, a big thank you to Kindred Arts.

    I am going to get KA's Ghost Lighting set, for ease of use, and in support of KA's contribution to my art efforts, but a little experimenting with the concept and settings laid out above proved how worthwhile this investment wll be, come payday.

     

    Post edited by nowefg on
  • KindredArtsKindredArts Posts: 1,041
    nowefg said:

    Just a quick note: I'm using 4.9 on a 2007 Lenovo T61, Core2-Duo, Invidia 140m onboard "graphics", and 2 gb accesible ram, with an SSD system drive and an outboard HDD data drive. I finally found a way to do a non-crashing Iray render, by setting a system-managed paging file on my outboard USB 2 HDD. The paging file has to go on the outboard, because paging is contraindicated for SSD's, so it does have to squeeze through that USB 2 bottleneck.

    This, I think, qualifies as "lower end hardware."

    I have struggled to get predictable interior light in a scene like KA is showing above, and have been wishing for an Iray option something like AoA's Ambient lighting, which I use in most 3DL renders. I've purchased a couple of Iray interior lighting sets, but they seem more suited to portraiture, and do great job at that, but I want the lighting freedom I'm used to in 3DL.

    I took KA's Ghost light tip, here, and was shocked at how well it works, and what subtle effects are possible, especially by using different colors on several ghost lights, like a blue coming in the windows on the shadow side of the room, and a golden light coming from sun-side windows. To do that deliberately, without trying to guess at what a given HDR is going to come up with and rotating ad nauseum, is a tremendous restoration of my artistic exhiliration. Just huge fun.

    The renders still take "a bit" more than 2 minutes, but what I get for waiting is so much richer and more fun than trying yet-another HDR and hoping it looks "kinda" like I "wish" it would. A couple of hours of experimenting with ghost lighting showed me I can do whatever and exactly what I want, even given the hardware constraints. Struggling about which side emits, I found that using a glaring color and blasting the luminence makes that easy to find out, and then rotate the primitive and switch to more nuanced colors and luminence. Experimenting with that "which side" process was such a trip, because it showed me I can do anything, exactly as I want to, and still have a lot of room for physically-based-light magics to happen in the mixing and bouncing of light interactions and reflective surfaces.

    So far, a simple-scene fifteen minute render is still quite grainy, and a one hour render needs more time, but a five minute tweak render shows enough to see how the lights are working and where the render is going, and stop to adjust ghost light angles and colors. To be realistic, I don't know how long it would take to get a smooth looking render like I see above, probably a few hours, if even then, but I do have confidence now that however long it takes, it will be the render I wanted. So, a big thank you to Kindred Arts.

    I am going to get KA's Ghost Lighting set, for ease of use, and in support of KA's contribution to my art efforts, but a little experimenting with the concept and settings laid out above proved how worthwhile this investment wll be, come payday.

     

    No problem, and thank you for such a thorough review. I know a lot of hobby artists work with incredibly tight budgets, and i felt quite guilty about hoarding such valuable information. I can't take credit for it though, this method has been around for a very long time, spanning several different renderers, i just tried to make it more accessible. My set on the store is designed to take a lot of the guess-work out of it, and includes a lot of physically accurate lighting presets. If anyone can't/doesn't want to purchase my set however, i'm still here to support anyone who has issues with this method.

    Glad to be of service, happy rendering!

  • hphoenixhphoenix Posts: 1,309
    barbult said:

    Very interesting. Is there a reason for setting the emissive panes to two sided?

    Nope, one sided is fine. This was aimed at beginners though, and i had a horrible feeling that they might place them the wrong way round and then shout at me because nothing was happening.

    I'd personally recommend AGAINST leaving it two-sided on......if there is glass behind it, and it has a realistic glass shader and thickness, the engine WILL calculate the light interactions through the glass, which will be slower.  Of course, with recessed windows like this, you might get unwanted darkening of everything behind the one-sided lighting.

  • AndySAndyS Posts: 1,362

    HI,

    on ShareCG I offer a free simple (GhostLight) shader easy to be applied to the light planes in windows, door, ceiling, ...

    --> https://www.sharecg.com/v/87021/browse/7/Material-and-Shader/Simple-iRay-GhostLights-Shader

  • Very helpful, thanks for sharing :)

  • I started with Daz end of August this year and I just got the Ghost Light Kit 2 now after someone recommended it. I am not sure if I am using the Kit in the best way, but I find it already very satisfying. I just use several light balls at around 50% scale and then adjust exposure value and intensity preset (kcd) to get enough light and I put light preset at 9000K which seems to give the most natural color(?). 

    Before using Ghost Light Kit, I spent quite a bit more time on indoor lighting using spot lights, so I am happy I got this now.

  • KindredArtsKindredArts Posts: 1,041

    I started with Daz end of August this year and I just got the Ghost Light Kit 2 now after someone recommended it. I am not sure if I am using the Kit in the best way, but I find it already very satisfying. I just use several light balls at around 50% scale and then adjust exposure value and intensity preset (kcd) to get enough light and I put light preset at 9000K which seems to give the most natural color(?). 

    Before using Ghost Light Kit, I spent quite a bit more time on indoor lighting using spot lights, so I am happy I got this now.

    Hey Dirk! Glad you like the set. 9000K is a light blue color. Lower kelvin units denote an orange/red color, whereas a higher value turns blue (6500 is neutral). Hope that helps.

  • Hey Dirk! Glad you like the set. 9000K is a light blue color. Lower kelvin units denote an orange/red color, whereas a higher value turns blue (6500 is neutral). Hope that helps.

    The first time when I used the light balls without any materials, the color became a bit yellowish. I attach some files below. The first render I made for this was with only light from the environment through the windows and to obtain a similar color with ghost lights, I had to apply 9000 K. Since then I always apply 9000 K.

    environment.png
    960 x 640 - 1M
    ghostlightnormal.png
    960 x 640 - 941K
    ghostlight9000.png
    960 x 640 - 954K
  • KindredArtsKindredArts Posts: 1,041

    Hey Dirk! Glad you like the set. 9000K is a light blue color. Lower kelvin units denote an orange/red color, whereas a higher value turns blue (6500 is neutral). Hope that helps.

    The first time when I used the light balls without any materials, the color became a bit yellowish. I attach some files below. The first render I made for this was with only light from the environment through the windows and to obtain a similar color with ghost lights, I had to apply 9000 K. Since then I always apply 9000 K.

    Yup, a higher value will work for skylighting (especially overcast light), and lower values for sunrise/sunset.

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