Short answer: A widely used rule of thumb is to place the diffusing acrylic at least as far from the LEDs as the LEDs are from each other, and about 1.5 to 2 times that spacing for a smooth, dot-free glow. For a strip with LEDs every 0.65 in. (60 per meter), that's roughly 1 to 1.3 in. of depth. Less depth needs denser LEDs, a stronger diffusing sheet such as white or Satinice-type acrylic, or an edge-lit design using light-guide acrylic, which can be as thin as 4 mm with LEDs along the edge.
Key facts
- Rule of thumb: diffuser distance at least equal to LED spacing (pitch); 1.5 to 2 × pitch for a uniform look.
- Why it works: Plexiglas notes that the smaller the distance between LEDs and the cover, the more likely hot spots are visible.
- Diffusing grades: ACRYLITE Satinice WD852 to WD855 at 2 mm transmit about 92%, 85%, 79%, and 72% of light, diffusing more as transmission drops.
- Edge-lit option: ACRYLITE LED light-guiding sheet comes 4 to 10 mm thick and lights panels up to 39 in. from one edge or 78 in. between two.
- Heat: keep any light source's heat well under acrylic's continuous limit of about 160 to 180 °F.
Why do I see LED dots through acrylic?
Each LED is a tiny, bright point aimed forward. Light spreads out as it travels, so the farther the diffuser is from the LEDs, the more each LED's cone overlaps with its neighbors' before it reaches the sheet. Too close, and each LED makes its own bright spot with dimmer gaps between. A diffusing sheet scatters light inside the material to blur those spots, but it can only do so much. Plexiglas puts it simply: the smaller the distance between the LEDs and the cover, the more likely hot spots will be visible.
How deep should my light box be?
| LED strip density | LED spacing | Minimum depth (1 × pitch) | Smooth glow (1.5 to 2 × pitch) |
|---|---|---|---|
| 30 LEDs/m | about 1.3 in. (33 mm) | about 1.3 in. | 2 to 2.6 in. |
| 60 LEDs/m | about 0.65 in. (17 mm) | about 0.65 in. | 1 to 1.3 in. |
| 120 LEDs/m | about 0.33 in. (8 mm) | about 0.33 in. | 0.5 to 0.65 in. |
| COB strip (continuous) | effectively none | very shallow | about 0.25 to 0.5 in. |
These are design starting points, not guarantees. Wide-angle LEDs need less depth than narrow ones, bright LEDs need more, and the sheet you choose shifts the numbers. Rows of strips should also be spaced about the same as the LED pitch. Build a quick mock-up with your strip and an offcut before committing to a frame.
Which acrylic diffuses LEDs best?
- White translucent acrylic: strong diffusion, lower transmission. The usual choice for sign faces and shallow boxes.
- Light-diffusing grades: ACRYLITE Satinice and PLEXIGLAS Satinice contain diffusing beads throughout the sheet. ACRYLITE's enhanced WD85X series trades transmission for diffusion, from about 92% (WD852) to 72% (WD855) at 2 mm. PLEXIGLAS LED makes backlighting grades in white and colors, 2 to 10 mm thick.
- Frosted or satin-surface clear: softens the image of the LEDs but diffuses less than bead-filled sheet, so it needs more depth. See frosted acrylic options.
- Clear acrylic: doesn't diffuse at all; every LED shows.
Two layers help when depth is tight: a diffusing sheet a short way off the LEDs plus a second face sheet. Light transmission numbers by color are in acrylic light transmission.
What if I don't have room for depth? Edge lighting
Edge-lit panels put the LEDs along the edge of a light-guide sheet instead of behind it. Particles in the sheet redirect light out of the face evenly, so the whole panel can be as thin as the sheet. ACRYLITE's LED light-guiding grades come in 4 to 10 mm and are matched to panel size: SM for panels up to 6 in. from a single lit edge (12 in. with two), L for 6 to 12 in. (12 to 24 in.), XL for 12 to 24 in. (24 to 48 in.), and XXL for 24 to 39 in. (48 to 78 in.). ACRYLITE recommends reflective tape on the edge opposite the LEDs, a polished input edge, and keeping posters from touching the sheet directly, since optical contact makes bright and dark patches. How this works: how edge-lit acrylic signs work.
Tips for an even glow
- Use the densest LED strip you can, or COB strip, when depth is limited.
- Paint or line the inside of the box white to bounce light around.
- Keep the LEDs and driver ventilated; acrylic's continuous service limit is about 160 to 180 °F.
- Polish the edges of edge-lit panels where light enters; ACRYLITE notes a polished end loses less light than a sawn one.
- Test with your actual strip before building the final enclosure.
We cut white, translucent, frosted, and clear diffusers and sign faces to size; see acrylic LED light diffusers or price a panel in the instant quote.
Questions
Can LEDs touch acrylic?
Low-power LED strips run cool enough to sit near acrylic, but leave a small gap and check the temperature at the sheet in a closed box. High-power LEDs and drivers can exceed acrylic's 160 to 180 °F continuous limit and need heat sinking and space.
Does thicker acrylic diffuse LEDs better?
With bead-filled or white sheet, yes: thicker sheet scatters more and transmits less. With clear or surface-frosted sheet, thickness makes little difference to hot spots.
White or frosted acrylic for an LED sign?
White translucent hides LEDs better at short depths and looks even when off. Frosted clear lets more light through and looks crisper by day, but needs more depth to hide the dots.