Two constructions, one job
COB strip mounts a continuous array of LED dies onto the FPC and seals them under a phosphor layer. SMD strip places discrete packages at a fixed pitch and solders each one. Both produce light along a line; the difference is what the viewer sees at close range and how much depth the detail can give you.
Where the difference becomes visible
Dotting appears when the pitch is wide relative to the distance between the strip and the surface it lights. On a shelf edge, under a wall cabinet or inside a shallow cove, the viewer is close enough to see individual emitters on SMD strip. COB reads as a continuous line because the emitting surface itself is continuous.
If the profile is deep or the diffuser is far from the strip, the pitch matters less. A 240 LED per metre SMD line in a 20 mm profile can read as smooth at normal viewing distance, at a lower cost than COB.
- Detail depth under 30 mm or viewing distance under 300 mm: COB is the safer choice.
- Cove with a deep return and an indirect view: high-density SMD is usually enough.
- Curved details: COB on a narrow FPC bends without a visible break at each package.
Output, heat and profile choice
SMD packages concentrate heat at each solder joint, while COB spreads it across the FPC. Neither is a problem when the strip is bonded to an aluminium profile, but a bare COB run at high power in an enclosed channel will shorten its life. Treat the profile as part of the thermal design, not just a decorative channel.
Per metre, high-output SMD is easier to source above 18 W/m. COB is usually chosen for uniformity rather than maximum output, and a 12 W/m COB line is often enough for a detail that the viewer stands next to.
A short decision sequence
- Measure the distance from the strip to the nearest visible surface.
- Decide whether the line will be seen directly or only as reflected light.
- Confirm the profile depth and diffuser type that fit the construction detail.
- Set the cut interval against the module length so the run ends on a cut mark.
- Agree the voltage, colour temperature and IP rating before sampling.
What to send with the enquiry
A section drawing, the target colour temperature, the total run length and the number of separate runs are enough to compare a COB and an SMD option on the same brief. Both should be quoted with the profile and driver that match the run, otherwise the comparison is not like for like.
Key takeaways
- COB solves visible dotting at close range; SMD solves output and cost in deeper details.
- Profile depth and diffuser distance decide how much the pitch is visible.
- Quote strip, profile and driver together so the comparison is equivalent.
