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COB vs SMD – light uniformity
Why light shows dots in a profile under 20 mm and how to prevent it.
What dotting means
The individual LED chips of an SMD strip are separate points of light. Today’s strips are already dense (e.g. TASAINEN 17W with 240 LED/m), so the dots blend as soon as they have some distance: in a profile over 20 mm the result is even. In a profile under 20 mm there is no distance, and the dots show through the diffuser.
In a COB strip (Chip on Board) the LED chips are packed into an even band of light with no visible dots. The light is dotless and even regardless of the depth of the bulkhead when it is switched on.
| Situation | SMD | COB | Choice |
|---|---|---|---|
| Profile under 20 mm | Dots on the ceiling | Even | COB required |
| Profile over 20 mm | Works | Even | Both are fine |
| Price / metre | Cheaper | Slightly more | — |
| Max power (low profile) | 14.4 W/m | 14.4 W/m | — |
Practical rule of thumb
If the profile depth from strip to diffuser is under 20 mm, choose COB. In a profile over 20 mm, today’s dense SMD strip works well. What decides is not the size of the bulkhead but the gap between strip and diffuser — in a low profile the light has no distance to blend.
Frequently asked questions
Which is better, COB or SMD?
For a profile under 20 mm COB is the only workable choice, because the strip is too close to the diffuser and the dots have no room to blend. In a profile over 20 mm, dense SMD gives the same even result for less. The deciding dimension is not the size of the bulkhead but the profile depth from strip to diffuser. But when it comes to how long a strip can be fed from one end, SMD always wins.
Do LED dots show on the ceiling?
They do if the strip is too close to the diffuser or the LEDs are sparse. Dots appear when the light of an individual LED has not yet blended with its neighbour’s. The solution is a deeper profile, a denser strip or a dotless COB.
What does COB mean in an LED strip?
Chip on Board: the LED chips are bonded directly to the circuit board and covered with a continuous phosphor layer. The light surface is a continuous line, not dots. That is why COB works in a low profile where SMD would show dots.
How many LEDs per metre are needed?
For an SMD strip, 120 LED/m is the minimum for indirect light and 240 LED/m gives a clearly more even result. For a COB strip the figure does not matter, because the light surface is continuous — LedStore’s SOLO strips have 280–512 LED/m.
Why is the light uneven at the ends of the profile?
The strip ends before the end of the profile because the cut point fell in the wrong place. Use a strip with a short cut interval, or LedStore’s “cut anywhere” strip so the length is exact.
Opal or clear diffuser?
Opal evens out the dots but takes 10–20 % of the light. Clear lets all the light through but reveals the dots. In indirect lighting a diffuser is often not needed at all, because the ceiling surface does the same job.