Quick answer: An uneven halo usually comes from LED pitch that is too wide, modules too close to the wall, a face that blocks light unevenly, or a wall that is not flat. Fix the pitch and diffuser first; changing the LEDs alone rarely solves it.
1. LED pitch
If modules are spaced too far apart, each one produces its own bright patch on the wall. A tighter pitch evens the glow but adds cost and heat. Large letters need more modules than their face area suggests because the halo spreads the light over a wider area.
2. Standoff and wall distance
Too little standoff concentrates the light into a narrow ring; too much dilutes it until the halo looks weak and grainy. The relationship is covered in halo letter standoff distance.
3. Face and diffuser
A face that is not uniformly diffusing, or a return that blocks part of the light, creates shadows. Check that the back opening is clear and the diffuser covers the whole letter, not just the centre.
4. Wall flatness
A wavy wall changes the distance between letter and surface, which changes the halo width. On rendered or panelled walls, a mounting rail that keeps a constant distance is more reliable than individual spacers.
How to diagnose
- Photograph at night from directly in front and from 45 degrees
- Measure module spacing against the drawing
- Check the standoff at several points around the letter
- Compare one letter with another; if only one is uneven, the issue is local
If the whole set is uneven, the design pitch is the cause; if one letter is different, check its wiring and diffuser. Construction detail is in reverse lit channel letters.