Understanding Filament Color Reflection and Transmission for Lighting Design

When it comes to designing lamps or other lighted objects with 3D printing, choosing the right filament is critical—not just for aesthetics but also for functional light diffusion. One surprising challenge in filament selection is how the same color filament from different suppliers or batches can exhibit vastly different properties when backlit.

The Mystery of Color Transmission

Imagine you’re working with white filaments. Under normal lighting, different brands may appear identical, reflecting the same bright white hue. However, when backlit with a white light, surprising differences can emerge. For instance, one filament might transmit a pure white glow as expected, while another could reveal a purple or lavender hue.

These differences in color transmission are due to the specific pigments, additives, and manufacturing processes used by filament producers. Even if two filaments are marketed as “white,” their light-transmitting properties may differ significantly, affecting the final appearance of your project. This phenomenon isn’t limited to white filaments—it applies to other colors as well, particularly those with subtle undertones or less common additives.

Light Behavior on Different Printed Surfaces

The way light interacts with your print isn’t just about the filament but also the geometry of the printed object. The surface type and thickness significantly influence light transmission.

1. Build Plate Surfaces: Surfaces printed directly on the build plate tend to have a denser, smoother structure due to the squishing effect of the first layer. This often results in reduced light transmission and may create a more muted or diffused glow.
2. Side Walls: Vertical walls, composed of thinner layers, allow light to pass through more readily. However, they often display artifacts such as layer lines or uneven diffusion that can alter the light’s appearance.
3. Top Layers: Depending on the infill pattern below, the top surface can have varying levels of opacity, leading to inconsistent light transmission. This makes uniformity an additional challenge in lamp design.

Designing Effective Filament Tests

To evaluate a filament's suitability for lamp or light designs, it’s important to test its reflective and transmissive properties under conditions similar to your final use case. Instead of relying on small swatches or generic test shapes, consider printing a specialized testing piece:

• Shape: A prismatic “L” structure works well, with one leg representing the flat surface of a base and the other acting as a vertical wall. This design allows you to assess how light behaves on both types of surfaces.
• Thickness: Match the surface and wall thickness to your intended use. For example, if your lamp walls will be 2 mm thick, ensure your test piece uses the same dimensions.
• Size: The test piece should be large enough to clearly observe light behavior. A small or overly thin model may not reveal the true differences in reflection and transmission.

Additional Considerations

• Light Source: Use a consistent and controllable light source during testing. LEDs with adjustable color temperatures are a great choice for experimenting with how the filament interacts with different lighting conditions.
• Batch Consistency: Even within the same brand, color and transmission can vary between batches. Always order sufficient filament for your project and test before committing to large prints.
• Post-Processing: Consider that post-processing steps like sanding or polishing can alter light transmission. Test filaments in both raw and finished states to get a complete picture of their potential.

Conclusion

Choosing the right filament for lamp or light design in 3D printing isn’t just about the visible color under normal lighting. Differences in transmission, influenced by pigment, additives, surface type, and geometry, can dramatically affect the final result. By using well-thought-out test shapes like prismatic “L” structures and carefully analyzing the behavior of light, you can ensure your 3D-printed creations shine—literally and figuratively.

Have you had surprising results with filament transmission? Share your experiences in the comments below!