I made an indoor scene in blender and now i want to render it with Luxrender, but i have a problem. I added two sun lamps and I want to let the first lamp shine through a glass door and the second lamp should shine through the window so you can see some shadows from the window on the floor. But after about 40 minutes of rendering the image was still very very noisy and the room was still too dark. Thats why i added a plane and added some emmit value to it (meshlighting) to light up the room. But after about 50 min. rendering the picture was still really noisy as you can see on the last image. What did i do wrong? Or do i have to render longer because my computer is to slow? (2 Ghz, 2 GB of RAM, windows xp). On the other pictures you can se my scene set up and the settings for the plane and the two lamps.
Are you using a portal on the window and door? It will help a lot when all your light is coming from outside. Put a planes covering the window and doorway, and make sure their normals face into the room (this is important), then under mesh options check the “Exit Portal” box. Which material you give the portal meshes won’t matter, it isn’t used.
Also, 2 sun lamps will quite clearly look like like “twin suns” in the render. This might be what you want, but the lighting will not be “Earth-like”.
And no, that computer is not terribly fast for Lux, so your image might be noisy for the first few hours. Keep an eye on the “eff” stat in Lux’s stats bar. Unless you are using photon mapping, that number should be at least a few hundred %, if not over 1000%.
I have not worked with LuxRender and use another unbiased renderer and believe my advice more or less applies to most unbiased render engines:
As J_the_Ninja already suggested you need to cover your openings with exit portals. these need to over the opening completely and the surface normals need to point into the room. Unless you have done that, this will greatly reduce render time.
Keep reflectances below 80% or 205 for each 8bit RGB color component. This will reduce the number of light bounces and will let you image converge faster. There are no materials in nature that have over 80% reflectance and even that was only measured on some special paper.
