what affects caustics intensity?

[EricR]

I am trying to get nice bright images of the sunlight that a mirror casts on objects. This is for a solar concentrator animation (power generation by focusing sun on boiler).

I can't get the intensity of caustics to reproduce from one object/scene to the next. I am using LW 10.

See comparison photos.
both have:
-accuracy = 10,000
-softness = 5
-spotlight 7.5 degree angle
-white target surface with 100% diffuse
-mirror surface with 100% specular, gloss, reflection
-light to mirror and wall to mirror distances are about the same.

But one is much brighter! I want the bright way to work always. Experiments with distance from mirror to wall show that this matters, but does not explain the extreme difference.

Any suggestions or explanations would be appreciated.

attached projects:
ControlledCausticsTest10 (dim)
CausticsRadiosityTestLW10 (bright)

[pixym]

Just some words: lw caustics are a nightmare if you want to have realistic results, I am very sad with them.

[shrox]

I had a similar dilemma, I ended up using spot lights with image projection.