A standard 12-inch front-lit channel letter with a 4-inch stroke and a 3-inch-deep can needs 4 to 6 SMD 2835 LED modules. That's it. Run more than that and you're either hiding a cheap acrylic face or you enjoy watching your power bill climb.
Look, I've worked the production floor at Aochuang Sign since 2010. I've built enough channel letters to know a clean glow from a lit-up waffle. The module count is where it starts.
Here's what nobody tells you: module count controls how the sign reads at night. Too few modules? You'll see dark bands at every stroke bend. Too many? You'll see bright spots through the face. Our standard 5mm acrylic transmits 90-92% of the light, so you can't hide a bad layout.
The ugly truth: module count also controls LED lifespan. SMD 2835 modules push 100-150 lumens per watt. Run them within rated current and they'll hit L70 at 50,000 hours. Overdrive a cheap module and you're replacing it in 12-18 months. I've pulled dead modules out of letters less than two years old.
The right module count turns a $2,000 sign into an $8,000 sign.
One module every 3 inches doesn't mean the same thing from letter to letter. A narrow stroke with a 2-inch can needs tighter spacing than a wide stroke with a 5-inch can. The light has to reach the face, bounce off the returns, and exit the acrylic evenly. If it doesn't, you get shadows and hot spots.
Space modules too far apart and the gap between them goes too dim for your eye. Space them too close and the face looks like a series of dots, especially with thin acrylic. That's not a sign; that's a test pattern.
I've watched shops sell 30 modules for a 14-inch letter with a 3-inch stroke. The client loved the brightness for a month, then complained about hot spots in photos. The real fix? 12 modules and a 5mm acrylic face from Mitsubishi or Degussa. Not 30 modules and a prayer.
Letter height is a crutch, not a measurement. A 24-inch "I" with a 2-inch stroke has maybe 4 linear feet of stroke. A 24-inch "W" with 3-inch double strokes can have 12 linear feet. Same letter height, three times the modules. Quote by height alone and you just lost your shirt on the "W" and overcharged on the "I."
Here's another thing nobody tells you: the type of acrylic face changes module needs more than most fabricators admit. A 5mm face from Mitsubishi or Degussa with 90-92% transmittance and UV inhibitors holds its clarity for 5-8 years. Domestic acrylic can yellow in 1-2 years, and once it yellows, everyone blames the modules. They're not the problem. The face is dead.
Can depth matters, too. A 3-inch-deep can concentrates light, so you need closer spacing. A 5-inch-deep can lets light spread before it hits the face, so you can stretch spacing by 20-30%. That's not a datasheet number; that's what I've measured on the floor with a light meter.
Module type changes the count, too. SMD 2835 is the workhorse at 100-150 lumens per watt. SMD 5050 is for RGB because it has three channels. SMD 5730 punches 40-60 lumens per chip and handles wider strokes. If you're lighting a 6-inch stroke on a 48-inch letter, 5730 modules at 4-inch spacing beat 2835 modules at 2-inch spacing every time.
A standard 3-inch-deep can with a 5mm acrylic face gets one SMD 2835 module every 3 to 4 inches of stroke. That's the rule I give new fabricators. If the can is 5 inches deep and the face is 3mm, I'll stretch to 4-5 inches. Deeper can, more spread.
A strip-mall storefront sign 18 feet from the road needs 100-150 lumens per square foot of acrylic face. Highway signage? Double that. Nobody ever calls to say a sign is too even. But they'll call if it's dim at 55 mph. These aren't published specs; they're what works when the customer calls back after 10 p.m.
Look, if you're doing back-lit or halo-lit letters, the rules flip. You're not pushing light through the face; you're bouncing it off the wall. You can often use 30-40% fewer modules than a front-lit letter of the same size because the glow is indirect. But don't cut corners on the power supply thinking you're saving money.
Get a scale drawing or mark the letter on the floor with tape. Trace the centerline of every stroke. Not the perimeter. The middle. That trace gives you your real stroke length.
Then pick your spacing based on can depth and module output. For a 3-inch can with 2835 modules, use 3.5 inches. For a 5-inch can with 5730 modules, use 4.5 inches. Divide total stroke length by spacing. That's your base module count.
Add 10% for bends, end caps, and terminations. If you have double-stroke letters, double the stroke length before you divide. If you skip that step, you'll have dark centers in letters like "W" and "M."
I've seen this go wrong: a shop quoted 312 modules for a 48-inch "M" because he used face area. The actual traced stroke was 22 linear feet. At one module every 3.5 inches, that's 75 modules. He had 237 extra modules left over. The client didn't pay for those. He did.
Then check the power supply. Size it at 80% of rated load, not 100%. A 12V system and a 24V system can change how many modules you can run on a single string, but not the total count. You still need the same number of modules to light the face evenly.
The table assumes front-lit letters with a 5mm acrylic face and SMD 2835 modules. Wider stroke, double stroke, or deeper can? Adjust up or down.
| Letter Height | Stroke Width | Can Depth | Modules per Linear Foot | Notes |
|---|---|---|---|---|
| 6–8" | 3/4–1" | 2–3" | 4–5 | Tight spacing, 2.5–3" between modules |
| 10–14" | 1–1.5" | 3" | 3.5–4 | Standard storefront letters |
| 18–24" | 2–3" | 3–4" | 3–3.5 | Bump to 5730 if stroke over 2.5" |
| 30–48" | 3–5" | 4–6" | 2.5–3 | Use 5730 or 5050 RGB for color |
Double-stroke letters? Multiply the linear footage by the number of strokes. It's not complicated, but it's the step most shops skip.
Rookie mistake number one is quoting by letter height and ignoring stroke width. I've seen a 24-inch "I" with 18 modules and a 24-inch "M" with 12 modules. The "I" looked like a runway light. The "M" looked like it had two black eyes. Same height, different stroke geometry.
The ugly truth is some fabricators over-space modules to win the quote. They'll put 8 modules in an 18-inch letter and tell you it's fine. It's not. The face will read uneven, and in six months you'll be back paying for a service call. Cheap modules make it worse. Dull gray solder joints are the tell: they won't last 18 months. Shiny silver joints mean proper lead-free solder and 5+ years of real lifespan.
I've watched sign shops pay $800 for a front-lit letter from a domestic fabricator. Same 304 stainless, same Samsung LEDs. We ship that letter from our 3,000m² floor in Lu'an for $120. That's the difference between buying through three middlemen and buying direct.
Another lie: "CE certified" means nothing if the factory can't show a certificate with today's date. CE testing costs 20,000-50,000 RMB. UL 48 runs $4,000-15,000 and takes 4-9 months with quarterly audits. If a factory says they have it and stumbles when you ask for the certificate, move on. We hold CE and UL, and I'll show you the paperwork.
When you buy modules with the sign, you should know exactly what's inside. We run Bluesky and Rishang modules, 5+ years real lifespan. Cheaper no-name modules fail at 12-18 months. If you're ordering front-lit channel letters for a storefront, don't let the factory bury a cheap module in a nice can.
We build at Aochuang Sign with 50+ workers and a 3,000m² facility. MOQ is one piece, and we still run every job through an 8-12 hour aging test and 100% QC inspection before it leaves. That means the module count you specify is the module count that actually works, not a guess from a sales rep who never touched a soldering iron.
Need a sample? Roughly 5 days. Bulk production? Around 15 days, depending on size and quantity. We ship express, air, or sea, and the crate gets handled 6-8 times on LCL sea freight. Pack it right or it arrives as scrap. We use foam, carton, and a plywood crate because I've seen what happens when you don't.
Guess and you'll be back in six months. Stroke length is the only reliable method.
Depends on stroke width and can depth. A 24-inch "I" might need 8. A 24-inch "W" with double strokes might need 24. Stop asking for one number.
No. Cheap modules die in 12-18 months. Adding more doesn't fix dull solder joints. Ask how I know.
No. It changes how many you can run on one string before voltage drop. Module count comes from stroke length and spacing.
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