Lighting advice needed

[S. Jaisimha]

Hi,

I'm trying to render the attached layout in AutoCAD using nXtRender and I am not sure how to get the lighting right. The drawing is Zipped to keep it within forum upload limits. I have attached a reference render generated in 3DS Max for the same layout.

The aim here is to get as close as possible to the lighting that is present in the 3DS Max render. Please ignore all props shown in the reference, as well as the lack of proper materials in the drawing. I'm only interested in getting the lighting right here.

Any help from you people will be greatly appreciated.

I'm not sure if this should be posted in the AutoCAD sub-forum, mods may please move it if necessary.

[George Ioannidis]

Looks like you are using nXt standard rendering engine (packet tracer). It produces somehow "not transparently looking" renderings. Try to use Path or Hybrid engine. Also it seems there is no external light (coming through the window). Materials have to be defined properly too, otherwise light condition calculation will be not accurate.

[S. Jaisimha]

Thanks George. Your advice about using Path or Hybrid engine is appreciated. My problem is how to specify proper lighting for interior scenes like this one. We can define an external sun light coming through the window in this case, but if there is no window, what should be done? 

In the above case, I had made the entire ceiling as one Area Light, but it doesn't seem to lead to very realistic images. How would you light the scene? Material definition is another aspect that I will research more into, but lighting seems to be my basic problem.

[Garret Diduck]

George has the right ideas to achieve what you are seeking. I would suggest spending a bit of time on your own to experiment with the lighting to get close to the results you want to achieve. 

If you are trying to mimic the Max scene, I would start with the Interior Daylight setting and work from there. Here is your model rendered with only 3 or so minutes worth of light tweaking. Most of that was trying to get the light from the sun on the floor to match the Max sample. I did not add any lights to your scene and used whatever you had in there to start.

[S. Jaisimha]

Wow, thanks Garret. I'll surely be spending more time on getting the Sun right! It seems to make a huge difference to the light.

[akinlolu olugboji]

You would also need more light than can come through the window by way of indirect light ie reflective surfaces rebouncing the limited light from the window.

[S. Jaisimha]

I added a sun to the layout and this seems to be the best I can do.

How can I get it to be soft like how Garret seems to have done above? Increasing Cloudiness doesn't seem to work properly. It now looks like this:

[Garret Diduck]

You're on the right track. I added cloudiness to the sun and reduced it's intensity as well. The image with the cloudiness looks pretty good so far. It appears that you are not using the Hybrid or Path Tracer engine. You'll see much better results using either of these in lieu of the Standard engine albeit at the expense of time.

[S. Jaisimha]

Thanks Garret. The reason why we are using the Standard engine is precisely because of speed. We want to see what can be achieved within say 15-20 minutes of rendering. Obviously that excludes the Path Tracer engine since it takes a very long time, preferably overnight or at least a few hours.

Anyway, could you give me some pointers on how to reduce the blackness that appears at the junction of the walls, especially where the ceiling and the vertical walls join? Adding more diffuse lights to the scene doesn't help much in this regard.

[George Ioannidis]

Though I am not Garret, I'll try to make a tip. It is by all means cheat, so it has nothing to do with exact light calculation of scene, it is just a trick to make your scene more "in light". Place a big area light behind the camera and try different light intensity for it, until it "fills" the room with enough "ambient" light. It is all matter of try and error procedure. I think it will give an improvement to what you are trying to do, though it is not anything accurate or proper.

[Garret Diduck]

I haven't used the Standard engine in quite a while, so I don't know how much help I'll be at this point. 

This image has only the daylight from the sun, no interior lights or 'cheat' (sorry George!). As you can see, the lights are indeed off and the image only ran about 32 passes. The corners are quite bright. The key is to turn up the ambient lighting to High and set the value to something that looks good. I used 24.0 here, but it might be a bit extreme as the corners are almost too white and are loosing definition.

[George Ioannidis]

Nice picture Garret. That solution has one big drawback for me. Having so very bright floor one could expect that enormous amount of light to bounce from the floor for instance to the vertical base of kitchen cabinets. Also all of the visible wall corners are gone, none visible. The window's wall is constantly gray, without any variation, which is not natural.

[Garret Diduck]

There are a few things going on here George that go against what you are thinking. The light on the floor is already indirect light. The sun through the window is only hitting the floor just in front of the lower cabinets by 25cm. So most of the light you are seeing in my image is indirect coming off the cabinets, counter and back splash wall.  So there wouldn't be much light coming back up off of the floor.

I agree about the quality of light, but I think that has a lot to do with the render engine and, to me, the materials. The materials in the attached model are not developed fully. I think the lighting would improve dramatically once that is accomplished. 

I also moved the indirect lighting number way up in my other image just to show what is going on. In this image, I turned it down quite a bit and tweaked some of the materials. You can start to see how the quality of the material starts to affect the lighting.