What Is a COB LED Strip? Construction and Limits
A COB LED strip bonds bare dies under one continuous phosphor layer, giving dot-free light. Construction, chip densities, cut lengths and when SMD is cheaper.
HFY Applications Engineering · Published September 2, 2026 · 3 min read
A COB LED strip is a flexible linear light in which bare LED dies are bonded directly onto the PCB and covered by a single continuous phosphor layer, rather than being packaged individually. This removes the visible dot pattern of SMD strip at close viewing distance. Production densities run from 320 to 504 chips per metre, typically on 24 V, at 8–15 W/m and CRI 90 or 95.
Key points
- COB removes the dot pattern by coating a whole row of dies, not by diffusing the source.
- Chip density sets the cut length: 480 chips/m cuts every 25 mm, 320 chips/m every 50 mm.
- COB costs 20–30% more per metre than SMD at the same flux, and is only worth it where the strip is visible.
- Copper weight, not chip count, decides how long a run can be before the far end dims.
What is inside a COB strip
An SMD strip starts with a packaged LED: a die on a lead frame, phosphor, and a plastic or ceramic body, soldered onto the FPC. A COB strip skips the package. The die is bonded straight onto the FPC, wire-bonded or flip-chip mounted, and the whole row is covered with one phosphor-and-silicone layer.
Two things follow from that construction:
- There is no pitch to resolve. The emitting surface is continuous, so at 100 mm viewing distance there is no dot structure to see, even in a 10 mm deep aluminium profile.
- The cut length is fixed by a die series. Because the phosphor covers a continuous row rather than discrete packages, the electrically separable unit is a group of dies — 25 mm at 480 chips/m, 50 mm at 320 chips/m.
Densities and what they mean
| Density | Typical power | Cut length | Best use |
|---|---|---|---|
| 320 chips/m | 8–10 W/m | 50 mm | Deeper coves, 15 mm+ profiles, budget projects |
| 480 chips/m | 10–13 W/m | 25 mm | Standard choice for profiles and cabinets |
| 504 chips/m | 12–15 W/m | 25 mm | High-output profiles, tight cut tolerance needs |
Higher density does not automatically mean more light per metre — it means the same light is spread more finely. A 504 chips/m strip usually runs at a lower current per die, which is why it lasts longer at the same wattage.
The trade-offs that matter
Cost. COB runs 20–30% above SMD per metre at matched flux and CRI, because die bonding is slower than pick-and-place and the phosphor process has tighter tolerance.
Diffuser depth. If the strip sits behind 3 mm opal acrylic, the diffuser removes the dot pattern anyway and COB buys nothing. The decision is optical, not fashionable.
Repairability. A failed COB segment cannot be reworked at component level: the whole 25 mm group is replaced by cutting and re-joining with a connector. On SMD strip a single failed LED can be swapped by a skilled technician.
Copper weight decides run length
A COB reel at 12 W/m draws 2.5 A over 5 m at 24 V. On a 1 oz FPC that run loses about 4.8 V and the far end is noticeably dimmer; on a 3 oz FPC the loss is about 1.6 V. This is why voltage drop is the constraint that limits long runs, not the chip count.
For projects where the strip is visible, COB LED strip is the right starting point. Where it sits behind a diffuser, SMD strip delivers the same result for less money — and saying so is the difference between a supplier and a salesperson.
What COB does not solve
COB does not improve colour rendering, does not increase efficacy, and does not remove the need for heat management. A 480 chips/m strip in a sealed profile at 60 °C still loses half its rated life, exactly as an SMD strip would. The construction changes how the light looks, not how the LED ages.
This article describes general manufacturing practice for machined and fabricated components. It is not a substitute for a drawing-specific engineering review — tolerances, material selection and process capability depend on the individual part.