Difficulties in Making Prototypes for Light Diffusion

diiusion prototype

Elon Musk once said, “If you don’t make stuff, there is no stuff”. It’s so simply-said, but so true. As a manufacturer specializing in prototyping, we have made a lot of “stuff”, all sorts of “stuff” from every industry imaginable. We are very proud to say that we have gained a lot of experience in making many parts. Yet we have encountered our fair share of trials and errors. 

This article mainly talks about the difficulty to imitate diffusing property during the prototype-development stage.

What is light diffusion?

The dictionary definition of light diffusion is “the scattering of light by reflection or transmission. Diffuse reflection results when light strikes an irregular surface such as a frosted window or the surface of a frosted or coated light bulb. The diffused light seems to wrap around objects. It is softer and does not show the harsh glares of direct light.

We have come across many customers that want to make a part that diffuses light. Behind or underneath the part, there is often a LED light source. Sometimes the part is soft material with certain hardness requirement. Sometimes the material is hard plastic.

How to make parts that emit diffusion lights

To make a plastic part diffuse light, one common way is to add light diffusion agent inside the plastic part during the injection-molding process or vacuum-casting process.

As you can tell from the photo below, “fine particles” are what we call “light diffusion agents”. These light diffusion agents generally are made of nano barium sulfate, calcium carbonate, silica, etc. When examined under a microscope, the diffusion agents are extremely small beads. Base resin can be clear PC, PMMA used for injection molding, or Polyurethane used for vacuum casting.

Photo from the Internet

Another common way to make a plastic part diffuse light is to coat a diffusion agent on the surfaces of the plastics.  For example, after a transparent PC or PMMA or Polyurethane part being made. A thin layer of glass beads (original glass beads are clear) could be blasted on the surfaces of the parts. In this case, glass beads serves as the diffusion agent. Another diffusion agent for this method is to spray clear grained paint, such as VDI36. The following part is a CNC-machined clear PMMA part. After it was being polished clear, VDI36 grained paint was applied.

The difficulty of making diffusing parts

As you might judge from the aforementioned methods to make diffusing prototypes, to make a part diffuse is very simple, the real difficultly is to make a part diffuse the right amount of light you’d like.

Full-Width Maximum (FWHM) and Half Angle (HA) are values generally used to quantify light diffusion and are commonly used to describe the light diffusion capability of plastic under a light source. For FWHM and HA, higher values mean a higher amount of light diffusion.

In a particular project we once had, a client specified the diffusion level FWHM to be bigger than 70°. Although we have made a lot of prototypes imitating the possible diffusion property, we were having difficulty making the part have a diffusion level to be over 70°.

For one thing, different shades of color, different wall thickness, different structures, different percentages of diffusion agents, and even different base plastic will cause a part to diffuse light differently. For example, if we have added a certain amount of diffusion agent in making a part during the urethane casting (or vacuum casting) process and we have met the requirement of the diffusion level desired by the client.

Then the next customer has a different part that wants the same diffusion effect. Even if this different part is only different in the wall thickness, we could use the same ratio of the diffusion agent as before, but we would not have the same diffusion results as before. Many attempts were needed to get the diffusion level right.

When moved on to mass production, the material used for parts of mass production will be different from the material used for prototypes. For instance, PC used for prototypes are block material while PC used for injection molding are plastic pellets. Although they are both called “PC”, they are in fact two different materials. PC plastic pellets have no impurities inside and are more heat-resistant than PC block materials.

Moreover, the methods used to make diffusing PC prototypes are different from that of mass-production (generally injection molding). The diffusion agent could be only coated on the surfaces of PC prototypes. While in injection molding, a diffusion agent is generally added to molten plastic during the molding process. After the parts come out of the mold, the parts will have a diffusion agent inside, which is what PC prototypes couldn’t do.


To conclude, although it is not hard to make prototypes that diffuse light, it will be extremely hard to make prototypes to diffuse a certain amount of light. Additionally, if applying the formula of the diffusion agent used in a prototype, the diffused light emitted by prototypes and parts of mass production will be different.

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