View Full Version : creating sunlight

12-07-2007, 03:32 PM
i'm having difficulty creating realistic lighting. at first i was creating multiple ambient light sources but the shadows were coming up too harsh and i needed about 30 sources of light to light the background (the landscape i'm using is huge) and the overall result didn't look that great because there were patches of bright spots and dark shadows. then i found this tutorial


the lighting looks great but the rendering time for each frame is taking about a day using the highest resolution for the camera and highest antialiasing. i'm guessing it's taking a long time because lightwave is calculating the reflections off the skydome. does anyone have any suggestions for creating realistic sunlight similar to the tutorial's but more efficiently?

thank you!

12-07-2007, 04:03 PM

The question you ask is dependent on a great many settings and factors, it is not easy to answer.
you are using radiosity, I presume, but with what settings? These settings can matter a lot.
What is your ray recursion setting, how complex is your landscape, what are those camera settings exactly, and are you sure you need to set it to the highest AA settings? That seems a little out of place, especially for a still you would only need the bare minimum of AA.

if you can post some examples we can help you more efficiently.

12-07-2007, 05:06 PM
yes, i am using radiosity. the settings are:
type: monte carlo
intensity: 100%
rays per evaluation: 6x18

i set my ray recursion limit to 16 with the render mode set to realistic.

the landscape is a desert terrain that was purchased from dosch design- a picture of it is attached. it's not that complex but it's big. it's about 3200 m x 3200 m, and i have a vehicle with 7 transparent and semi reflective windows, which i'm assuming is also increasing the rendering time.

the camera's setting is set to HDTV 1920x1080 for some stills and vga 640x480 for some others.
and antialiasing i set to enhanced extreme
reconstruction filter: mitchel(sharp)
everything else i left at its default values

i guess i don't need to set aa to the highest right now, but i'll eventually be making a simple avi of the vehicle going through the terrain.

thank you for your help!

12-07-2007, 05:49 PM
Which version of LW are you using? Given that your MC radiosity is set to 6x18 RPE, I'd assume you're on pre-9.2. If it's possible (iow, if you're on 6.x, 7.x, or 8.x and can afford the upgrade) I'd suggest upgrading. The 9 cycle has seen some remarkable enhancements to both render and radiosity speeds so far.

Otherwise, try playing with some of the settings - for an outdoor scene as in the .bmp posted, Background Only radiosity may get the job done in a fraction of the time, and Enhanced Extreme anti-aliasing wasn't always necessary, depending on the render and the output medium and resolution.

edit - just re-read your post. It's rarely actually necessary to set the Ray Recursion Level to 16 - not sure if it'd make any difference in a scene without noticeable reflections, but the RRF setting can kill a scene unnecessarily pretty easily. I usually use between 4 and 8 and it seems to be fine, but others may have different opinions on an optimal setting,

12-07-2007, 10:15 PM
As Maxx says, you want to upgrade your Lw version to 9.3.1
Then, you might want to read the tutorials in my signature on radiosity and AA. There's much to learn..

perspective camera not classic camera
Interpolated FG or Background only radiosity, not Monte carlo
Lower ray recursions
AA set to 3, AS to 0.03

12-07-2007, 10:17 PM
Ditto on the ray recusion, it's probably fine with 4, 16 can potentially double your rendertime, and only make a few pixels difference.

If you want sunlight, use a Distant light.

You may not need extreme AA and 6x18 rays per evaluation at the same time. Low radiosity settings like 3x9 will be grainy without AA, but with High AA it will be smooth. Setting them both really high is unneccesary.

For 'skydome' type renders you can save even more time by using Background radiosity instead of MC. Background radiosity didn't exist when that tutorial was made, probably 8 years ago. It calculates backdrop color only, not geometry, so it's much faster, and you'll have to remove the dome or it won't work -

12-07-2007, 10:55 PM
Is loading an HDR into the background and using Background Only Radiosity not an option? Or using the 3rd party Skylight procedural (can be found listed in the plug-in database on Flay.com)? If you have 9.3.1 you can even benefit from the pre-render GI blur. I've gotten some great results using this, renders very fast and the skydome can still be left in to provide reflections if you need, although a reflection map would probably render faster. If you need a directional light to cast your shadows you may want to turn down the radiosity to 50-75%.

Make sure any features you don't need are turned off in the Render Global panel such as lens flares, 2-sided Area Lights, Reduce Noise, Directional Rays (GI tab), etc. If you keep the skydome, make sure all its shadow rendering options are turned off. You can also turn off any lighting for it if you want as long as its luminosity is high enough to be visible even unlit.

Maxx is right, unless you have a ton of reflections or transparencies on your vehicle you won't need more than 4 to 6 rays. Again, this can be reduced by judicious use of reflection maps to 3 or even 1 for distant shots. Ray Tracing+Spherical map works wonders, just load the skydome texture in as the reflection map, the terrain will still render in reflections even with 3 rays.

Your AA settings could probably take a step or two down. Especially with the lower res images. Who is your target audience? Will they notice if you remove one level of AA? Two? If you sacrifice AA settings you may be able to add more realism such as fog or LW's fantastic Photoreal Motion Blur.

Out of curiousity, why the Mitchell reconstruction filter? I don't use these much, and I was wondering if you could share some of your reasons for using something other than Classic.

Last question: Are all your models regular polys or are you using sub-D surfaces? If you are using sub-Ds you may be able to shave off a few thousand polys by using either Per Poly or Per Object APS settings with a gradient based on distance to camera, angle to camera Z axis, or both. If the object is sub-D but your camera will be close for all shots it may be worth your time to freeze the mesh at the level you desire and remove any unnecessary geometry (large flat areas that get subdivided into hundreds of polys, etc). If the camera can't see it and it doesn't cast a shadow or reflection in your scene you don't need it. This is especially true for internal geometry which should be minimal at best.

Hope some of this helps.


12-08-2007, 03:33 PM
I use an area light. One sided, set 93,000 units (km, miles, etc.) away, and set to 1000% size. Raytraced shadows. The intensity set to about 115% to 130%, depending on time of day I want to sim. The color is very pale yellow, slightly shifted towards orange, almost white, but not quite. I then attach that to a null, then I can just rotate the null to place the light in the sky, usefull if you are using a texture mapped sphere or dome as the sky, makes lining up the bright spot much easier. That with a blue sky texture map for radiosity, and it looks pretty good.