How do I save a completed render as a .jpg or other image file? It only allows me to save an .flm extension.
Do renders in Lux take a long time? (typical time estimates, please?) I have been rendering one scene for about three hours now, and the product looks done. Does it auto-save, or do I have the option of saving it as an image?
There is an auto-saving image. Your last rendered image is in a directory that you can set in the LuxBlend script, under the System Panel (the second path to fill). Your image is there !
You can also choose to continue rendering, while exporting the rendered image of the moment. Simply find the Copy-Paste button that laid on the right of the Play, Pause, Stop and Threads buttons (3rd row on the upper left corner of LuxRender User Interface).
Saving a .flm won’t give you an image, but will permits you to continue rendering later, reopening it.
Rendering times depends on scene complexity, on computer’s capabilities and rendering choices (picture size, samples, etc…) and so on, but it is often seen rendering times up to 10 or even more hours…
LuxRender is an unbiased renderer; it simulates real light bouncing around your scene and so has to do an extraordinary number of calculations. A model with 4M verts can take 10 hours to render but you can get a decent render in 15 minutes on a 10K vert model.
A rough guide to rendering quality is the samples per pixel - S/px - on the bottom of your LuxRender window:
250 S/px - fair
500 S/px - acceptable
2000 S/px - good
3000 S/px - best
5000 S/px - you’d hardly notice the difference
Maybe some nice estimates but it is not that easy. It really depends on the rendering method you’re using (bidir’s samples are way slower than Path’s but also “better” in many cases) and on the objects / materials in your scene. A lot of indirect Light, Refraction, Dispersion, Caustics and similar stuff need a lot of samples, sometimes even 3000 are not enough.
So, such tables are not very reliable, if you ask me, but probably some nice first approximations (same goes for the rendertime…). Please keep that in mind, as karla said. (Just wanted to make sure…)
Oh, and on topic:
Yeah, it automatically saves the images to the path specified and does so on closing the render window, too 
Thanks for the info, everyone. Now I have a better perspective.
A final question. Which file is the actual image? Right now, I have four files related to the scene. When I finish rendering, does one of the files convert to a save image, or do I have to do it separately?
EDIT: Wait, I found it right under the other files. Whoops!