I think I have a useful variation of BB's idea for night shots, at least for P8+, since it exploits IDL.  My Lothlorien-esque stairway models have a lot of lamps, and dealing with eighty point lights is a chore (and a render burden).  :(   I recalled the thread here regarding ambient-textured geometry used to light a scene, but the panels had to be searing blown-out white, even though the light they cast was modest.
     After several trial experiments, I finally managed to get an idea to work:  an intense IDL emitter hidden inside a gently-glowing lamp.  Using this method, you only dial the default scene lights down;  no other lights are needed - the emitter geometry does the work in IDL.  For day shots, you need only uncheck the visibility box for one item - the emitter array is a single prop. :)
     Here is a test render of the top flet on the gnarly mulberry;  default Poser scene lights are dialed down to 8%, rendered in P8 with 4 raytrace bounces at 90% irradiance cache:

Attached Link: knothole nap

• The gently luminous lamp surface must be a discreet prop, separate from any lampstand/hanger parts.  The glowing surface must be visible, not cast shadows, and not visible in raytracing.  It can be opaque.
• The hidden emitter must also be a separate prop.  It must be visible, not cast shadows, and it must be visible in raytracing.  An ambient value of 20 for the emitter seems to work well in most situations.  Increase the emitter's ambient value to cast more light.
• The rest of the model would generally be visible, cast shadows, and be visible in raytracing.
• Render with IDL engaged.  More raytrace bounces will even out the lighting and fill deep shadowed areas better, but the render time cost increases asymptotically with more raytrace bounces.

     Link shows the knothole of the same huge mulberry tree, used as a napping cubbyhole, with a single nightlight.  ^^

     This is a raw Silo modeler screen capture of the mulberry tree with its stairway...

Attached Link: elvish apartment flets in mallorn tree

Wow! I love the feeling-tones in your images... what magic, Seachnasaigh! Very nicely done... and thanks for the tips!