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Hi,
I've got a strange effect.

Here a simple scene with/without a glass box (wizard glass).
The glass transmitance is a pur white, roughness 0, attenuation at 10 m...
The scale is ok, the thickness box is 1 cm.
The bottles material is a simple light blue wizard plastic.

With the glass box, everything inside the box is black, exept reflectives BSDF.
Its a problem with shadow?

gif for demonstration ( SL:18 / Maxwell 2.7.2 )

the problem comes from the roughness.
Here a test with a single green BSDF.
I put a map on the roughness.

when the roughness is close to 100, the material is black.
when the roughness is close to 0, we can see the reflectance color.

NL, i can send you the mxs if you want.

gif ( SL:18 )

the problem clearly appears when the roughness is greater than 50%.
This poses a problem for any composites materials with a diffuse base like plastic.

Wow
I certainly found an explanation. ( thank to roch_fr )

My emiters were in mode "hidden from global illumination"
I do not understand why this has solved the problem, but it works like that!

Any suggestion?

Problem in a box stays in a box.

Yes, sorry for that