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So we are developing a plastic case, where we want light to be diffused through the case. The light is kept 2-3 mm away from the inside wall. I wanted to know what thicknesses allow passage of light, and also what colors allow better diffusion. I have seen a couple of products which are in White. But otherwise there is usually a light pipe for the diffusion.

Update:

Material most likely will be ABS+PC or just ABS. presently design is 1mm. we are thinking that particular area reduce thickness a bit and keep a provision for a cylinder to block light from diffusing to other areas. Any idea on what mix would be the best? or if color will also affect the diffusion. I cant recollect any black abs part which diffuses light. Only white I have seen.

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  • $\begingroup$ Do you specifically want transparency or translucency? Transparent being the transmission of images, and translucency being the transmission of scattered light with no images. $\endgroup$ – wwarriner Apr 27 '16 at 17:43
  • $\begingroup$ translucency. because there is a pcb inside, you dont want to see that. and we were seeing if we could try various colors. Just led indicator lights have to be visible $\endgroup$ – albseb Apr 28 '16 at 4:57
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The answer isn't as simple as thickness alone. The material must be designed in such a way as to allow light but not images to pass through whatever designed thickness is acceptable. First figure out the mechanical requirements, then select a material which has a crystallization fraction that is both manufacturable and allows the required amount of light through at that thickness.

I am unaware of a general formula for thickness versus transmission of light through polymers since processing history plays a large role.

Some tradeoffs to consider...

  • Increasing thickness means slower cooling rates and thus larger crystal fraction, more crystallinity, and less transmission of more scattering)
  • Less crystallinity means more brittle behavior, lower material stiffness, and higher thermal distortion and creep rates
  • Thicker walls mean more global strength and stiffness (as opposed to material strength and stiffness)
  • Choice of material affects the ability to form crystallites, and all thermal and mechanical properties
  • Opaque filler can be used to reduce transmission but can increase brittleness and strength, may require testing to optimize.

A common choice for electronics housings is ABS which always scatters light due to in-situ rubber microparticles and high impact toughness and dimensional stability at room temperature. Again, due to processing history effects, there is no general formula for thickness versus transmission, so you will probably need to test.

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  • $\begingroup$ So from the things i have seen, the thickness was ~1mm. It was white in color, and it was a mix of ABS and PC. My worry was if only white color mix allowed transmission of light. my worry being a part in black wont let the light out, or as far as i have seen thatrs the case. This will be injection molded. $\endgroup$ – albseb Apr 28 '16 at 13:27
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    $\begingroup$ This is a difficult question to answer directly as there are a lot of variables. You may just have to experiment. If you can't experiment (e.g. you don't have the equipment), you might try contacting injection molding part manufacturers to ask for help. If you plan on making a lot of these, you could use that as leverage for getting more detailed answers. $\endgroup$ – wwarriner Apr 28 '16 at 19:56
  • $\begingroup$ thanks. Mostly we will go ahead with ABS + PC itself. Need to speak to a few manufacturers regarding color. $\endgroup$ – albseb Apr 30 '16 at 18:37

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