Choosing the Right Sheet for LED Lighting
Opal acrylic is a milky-white translucent sheet that scatters light so it glows evenly and hides the LEDs behind it. Light transmission, given as a percentage, tells you how much light passes through: a lower figure hides bulbs better but looks dimmer, while a higher figure is brighter but shows hotspots more easily.
If you are building a light box, illuminated sign or LED panel, opal acrylic is usually the face material. The trick is matching the light transmission to how far your LEDs sit behind the sheet. Here is how to get it right. For the wider colour range, see our coloured acrylic buyer’s guide.
What is opal acrylic?
Opal acrylic is standard acrylic (PMMA) made in a translucent milky white. Rather than letting light straight through like clear acrylic, it scatters the light across the whole surface. That even glow is why it is the go-to material for anything lit from behind, and why a lit opal panel looks like a smooth sheet of light rather than a row of bright dots.
How does light transmission work?
Light transmission is the share of light that passes through the sheet, written as a percentage. A sheet rated at 36% lets about a third of the light through; one rated at 70% lets most of it through. The lower the figure, the more the sheet diffuses and the better it hides the light source, at the cost of some brightness. The higher the figure, the brighter and more efficient the panel, but the harder it is to hide individual LEDs.
| Light transmission | Effect | Best when |
|---|---|---|
| Low (around 30–40%) | Strong diffusion, hides LEDs well, softer glow | LEDs sit close behind the sheet |
| Medium (around 50–60%) | Balanced glow and brightness | Moderate gap between LEDs and face |
| High (around 70%+) | Bright, efficient, but hotspots show more | Deeper light boxes with more space behind |
How do you choose the right opal for LED lighting?
The key factor is the distance between the LEDs and the sheet. When LEDs sit close behind the face, as in a slim light box or edge-lit panel, choose a lower transmission such as around 36% so the diffusion hides the hotspots. When there is more depth behind the sheet, a higher transmission gives a brighter result without showing the bulbs. If in doubt with a shallow build, go for stronger diffusion; a slightly dimmer, even glow always looks better than a bright panel dotted with hotspots.
What is opal acrylic used for?
Opal acrylic is used for illuminated signs and shop fascias, light boxes and menu boards, LED ceiling and wall panels, backlit displays and exhibition stands, and diffusers for light fittings. Anywhere a light source needs to look like an even glow rather than individual bulbs, opal is the material that does it. It is a mainstay of coloured acrylic signage.
What thickness of opal acrylic should you use?
3mm suits most signs and smaller light boxes. 5mm is a common choice for larger panels and ceiling installations, where it resists sag across a wider span and diffuses a touch more. For big unsupported panels, go thicker or add support to stop the sheet bowing over time.
Frequently asked questions
What does opal acrylic light transmission mean?
It is the percentage of light that passes through the sheet. A 36% opal lets about a third of the light through and diffuses strongly, hiding the LEDs. A higher percentage is brighter but shows hotspots more.
Does opal acrylic hide LED strips?
Yes, that is its main job. The translucent surface scatters the light so individual LEDs blur into an even glow. Lower light-transmission opal hides them best, especially when the strips sit close behind the sheet.
Is opal acrylic the same as frosted acrylic?
They are similar but not identical. Frosted acrylic has a textured surface that diffuses light; opal is coloured through the sheet to a milky white. Opal usually gives a more even glow for backlighting.
Can opal acrylic be used outdoors?
Yes. Like other acrylics it is weather-resistant and holds up in external illuminated signage, which is why it is widely used for shop fascias and outdoor light boxes.
What colour does opal acrylic glow?
Opal itself is white and takes on the colour of the light behind it. White LEDs give a clean white glow; coloured LEDs colour the whole panel evenly.
Order opal acrylic cut to size
We cut opal acrylic to your exact panel sizes, delivered across the UK. Browse the coloured acrylic range or tell us your light transmission and sizes and we will sort the rest.