PETG backlit signage is bought for one reason: an even face. Everything else, including the print, depends on the sheet diffusing light well enough that the customer never sees the LED grid behind it.
A sign shop in Chicago produced 180 illuminated shopfront signs with 3 mm opal PETG faces. Twelve were rejected by the client for visible banding, and all twelve shared a common cause: the LED pitch had been changed to save cost without changing the sheet.
PETG backlit signage sheet and transmission
- 2 mm opal: 30 to 45 percent transmission, small faces
- 3 mm opal: better diffusion, faces up to 600 x 400 mm
- Textured or matte face: hides hotspots at short standoff
- Printed face: second-surface print on clear sheet over the diffuser
Transmission is the number to agree with the sign designer. A 40 percent face over a 100 mm LED pitch at 40 mm standoff reads even; the same face at 15 mm standoff shows banding. The sheet cannot fix a geometry problem on its own.
Standoff, pitch and the thermoformed face
The rule of thumb that works: standoff should be at least 40 percent of the LED pitch. A 100 mm pitch wants 40 mm or more between the diodes and the face. Below that, either reduce pitch or add diffusion.
Thermoformed faces, common on petrol station canopies and fascia signs, change the problem because the draw thins the sheet. A formed face can be 30 percent thinner at the centre, which shows as a bright patch. Thicken the starting gauge, or accept the variation and design the LED layout to compensate.
Heat and ageing are the long-term considerations. A sealed box with a hot driver will yellow any plastic face. Ventilated boxes and remote drivers are the reliable detail.
Where the sign face sits over an acrylic light box body, the fabrication overlaps with acrylic sheet for LED signage, and the print and mounting details are covered in the acrylic LED light box guide.
For point-of-sale units that light up at the counter, the design logic overlaps with PETG POS display.
Send your sign size, LED layout and transmission target to oversales@rpplexiglass.com for a sheet recommendation.
Frequently Asked Questions
What transmission should a backlit sign face have?
Typically 30 to 45 percent for an opal PETG face with a standard LED grid. Higher transmission gives brightness but shows the LEDs; lower transmission evens the light but wastes output.
How do you stop LED hot spots on a sign face?
Three levers: increase the distance between LEDs and the face, reduce the LED pitch, or use a more diffusing sheet. A 2 mm opal face at 40 mm standoff hides a 100 mm pitch; at 15 mm standoff it does not.
Does PETG yellow behind LEDs?
Less than acrylic in most cases, but heat matters. LEDs run cool compared with fluorescent tubes, so a well-ventilated sign box keeps a PETG face clear for years. A sealed box over a hot driver will yellow the sheet.