@gadzooks:
(1) place some thin long surfaces (emitters {I have used a texture here to, a yellowish image with darker edges}) behind a big surface (plastic, sss1, abs0, color white);
(2) render a top view of only this;
(3) take this rendering and clean the image per denoise and gaussian blur;
(4) build a mxi texture from the image (3) with an intensity approx. 20;
(5) use a light box with two parallel surfaces same size for emitter (with the prebuilded mxi (4)) and glass for reflections direct above (color white, ND 1.5, abbe 200) - here I miss bump maps for dielectrics
(6) for your ready to use rendering use a burn 0 and a stronger gamma, so you keep the details in the light box texture and you get enough light in the scene
Extra hint: if somebody try to use a light box with a geometrie from (1) direct in the scene, make the inside of the box black. So, less noise will be produced, because the light dosn't bounce so much.
@Mihai: Thanks. I have try it befor. A wider angle bring me to much room distortion and the light of the box get to much attention, because it will more dominant in the foreground than the tricycle. I have rendered much previews befor.
@marumari; Sorry, the texture is a modfied not free texture from total textures. Textures - the workflow in maxwell is a little bit crazy. If I try to get a brighter texture, I must adjust the image and not a scale factor. But we will get it in the future.
@michaelplogue: Stringers? Must be a western variation of the tricycle. Here my one is only like in the picture. In the DDR (GDR) things was most more simple as in the west part of germany.
Thanks.