Nine out of ten problems with neon flex letter signs are geometry problems, not electrical ones. The tube kinks in the tight corner of an “e”, the light pulls away from the channel, or the edge looks lumpy where the radius was forced. All of it comes from ordering a profile without checking its bend radius against the letter stroke width. Here is how to do that calculation before you order.
Three numbers that have to agree
Stroke width is the width of the letter’s spine — the thickness of the line the designer drew. Profile width is the width of the neon flex across the bend plane. Minimum bend radius is the tightest inner radius the profile can take without kinking, folding or stressing the LED joints.
The relationship is simple once you see it. In a letter shape, the inner radius available at any corner is roughly half the difference between the stroke width and the profile width:
Available inner radius ≈ (stroke width − profile width) ÷ 2
If that number is smaller than the profile’s minimum bend radius, the letter cannot be made in that profile. No amount of careful bending will fix it.
Working numbers by profile size
| Profile | Min inner radius (horizontal bend) | Usable stroke width | Typical letter cap height |
|---|---|---|---|
| 6 × 12 mm | 25–30 mm | 80 mm+ | 100–200 mm |
| 8 × 16 mm | 30–40 mm | 100 mm+ | 150–300 mm |
| 10 × 20 mm | 50–60 mm | 130 mm+ | 250–450 mm |
| Round 15 mm | 40–50 mm | 100 mm+ | 150–300 mm |
| Round 20 mm | 60–80 mm | 140 mm+ | 250–400 mm |
| Round 30–40 mm | 100–150 mm | 250 mm+ | 400 mm+ |
These are working ranges, not datasheet absolutes. Every manufacturer’s silicone formulation behaves slightly differently, and a profile that takes 30 mm in a warm workshop will struggle at 30 mm in a cold one. Treat the table as a starting point and confirm against the supplier’s own bend test data for the exact profile.
Horizontal versus vertical bending
Profiles bend in one plane. Horizontal bending lays the tube flat in the plane of the sign — what you need for letters read face-on. Vertical bending curves the tube out of that plane, for ribbon shapes and contour work. The bend radius for vertical bending is usually *larger* for the same profile, because the tube is being bent the hard way across its height rather than its width.
Ordering a horizontal-bend profile for a vertical-bend job is the most common purchasing error in this product category. If a letter needs both — a script “S” that curves in two planes — it has to be split into sections and joined, which is why side-view and top-view profiles exist as separate products rather than a single universal tube.
What happens when you bend too tight
- Kinking — the jacket pinches, the internal cross-section collapses, and the light shows a dark band at the corner
- LED joint stress — the flexible PCB stretches on the outside of the bend, cracking solder joints. Failure appears weeks later, not at install
- Jacket whitening — over-stressed silicone turns cloudy at the bend, which reads as a bright patch at night
- Adhesion failure — the tube lifts out of its channel at the curve, leaving a visible gap
All four are irreversible. There is no field repair for a kinked profile — the section has to be replaced.
Five ways to make a tight letter work
- Go down a profile size — a 6 × 12 in the tight corners instead of 8 × 16, accepting lower output
- Increase the stroke width in the artwork — often the cheapest fix, and the customer rarely notices a 10 % bolder letter
- Split the run — bend the easy sections in one piece and join at the tightest corner with a short straight insert
- Use a shorter LED pitch — denser LEDs are more forgiving in tight curves and avoid a visible dark corner
- Pre-form the bend in the workshop, not on site at height
Dot pattern in tight curves
On the inside of a tight bend, LEDs compress together; on the outside they spread apart. With a 60 LED/m profile this reads as a bright inner edge and a dark outer edge on anything under about a 60 mm radius. Denser profiles — 120 LED/m and above — distribute the light far more evenly and are worth the extra cost on small letters. This is the practical reason to specify pitch by letter size rather than by price per metre.
Cutting and capping
Every profile has defined cut points, usually marked on the back every 25–50 mm. Cutting outside them leaves a section of LEDs unconnected and dead. The cap is the second failure point: a crimped and glued cap on a horizontal-bend profile will fail at the bend if the cap sits within the radius. Keep caps on straight runs wherever the layout allows, and use factory-moulded caps on any outdoor sign.
Signage specification checklist
- Stroke width at the tightest corner, measured from the artwork — not the average
- Profile width that leaves a positive inner radius at that corner
- Bend direction required, horizontal or vertical, per section
- LED pitch matched to the smallest letter cap height
- Number and location of cut points and caps
- Indoor or outdoor — silicone jacket and moulded caps if outdoor
- Voltage and run length per letter, with the driver position
Send us the artwork with the stroke widths called out and we will tell you which silicone neon profile fits each letter, where it has to be split, and what the bend radius means for your LED pitch. It is a ten-minute check that prevents an entire sign being remade.