How to Specify LED Strip: Six Numbers That Decide It
A specification checklist for LED strip: flux per metre, CRI and R9, SDCM, voltage and run length, IP rating and L70 at case temperature. With a template.
HFY Applications Engineering · Published September 22, 2026 · 4 min read
A usable LED strip specification states flux per metre at a given CRI and CCT, the binning tolerance in SDCM steps, voltage and maximum run length, IP rating with installation conditions, and L70 life at a stated case temperature. Six numbers, all measurable, all verifiable against a test report. Anything else on the datasheet is marketing copy.
Key points
- Flux quoted without CCT and CRI is not a specification — the same strip varies 40% across those two variables.
- CRI hides red rendering; R9 must be specified separately or the result will be a strip that makes red look brown.
- L70 without a case temperature is meaningless; a sealed profile runs 20 °C hotter than the test condition.
- IP67 does not mean chemical resistance, and it does not mean the driver can sit in the wet zone.
The six numbers
| # | Number | Example | Why it matters |
|---|---|---|---|
| 1 | Flux per metre at stated CRI/CCT | 1,150 lm/m at CRI 90, 3000 K | Sets illuminance; varies 40% across CRI and CCT |
| 2 | CRI and R9 | CRI 90, R9 ≥ 50 | Determines whether colours look correct |
| 3 | SDCM | ≤ 3 within a project | Determines whether adjacent runs match |
| 4 | Voltage and max run length | 24 V, 10 m from one feed | Determines the electrical design |
| 5 | IP rating with installation conditions | IP67, jets and temporary immersion | Determines whether it survives |
| 6 | L70 and case temperature | L70 50,000 h at 45 °C | Determines whether it lasts |
If a datasheet is missing any of these, the quotation is not comparable to another supplier’s quotation, and the difference will appear on site.
Number 1: flux, and why the datasheet misleads
A 2835 strip at 120 LEDs/m and 14.4 W/m can be quoted at 2,100 lm/m at CRI 80, 4000 K — or 1,450 lm/m at CRI 95, 2700 K. Both are honest figures for the same physical product family. Specifying “2,000 lm/m” without the conditions allows a supplier to meet the number with the cheapest bin.
Write the requirement as: 1,400 lm/m minimum at CRI ≥ 90, 3000 K ±100 K, measured to LM-79 on a 0.5 m sample.
Number 2: CRI is not enough
CRI is an average of eight pastel test colours and deliberately excludes saturated red. A strip can score CRI 90 while rendering red at R9 = 12, which is why red garments look brown and timber looks grey under some nominally high-CRI strip.
For retail, hospitality and residential interiors, specify CRI 90 + R9 ≥ 50 as a pair. For fashion and food, R9 ≥ 60.
Number 3: SDCM, the project-level number
SDCM is a per-reel property, but the specification that matters is project-level: how many reels will be visible together, and will they come from one production lot?
- Single room, one reel: SDCM 5 is fine.
- Continuous cove, multiple reels: SDCM ≤ 3, one lot.
- Multi-phase project over months: SDCM ≤ 2 with a reserved bin.
The mechanics of binning are covered in colour consistency for LED strip.
Number 4: voltage and run length, stated together
“24 V” alone says nothing useful. The specification must say maximum run length per feed at the specified wattage and copper weight. A 24 V strip at 15 W/m runs 6 m from one feed; the same strip at 8 W/m runs 11 m. See voltage drop for the calculation.
Number 5: IP rating plus conditions
IP67 is a test result for jets and temporary immersion, not a warranty against a pool environment or a chemical wash-down. Write the installation conditions into the specification:
IP67 silicone extrusion, mounted in a drained aluminium channel, driver in a separate IP65 enclosure outside the wet zone, cleaning with pH-neutral products only.
That sentence prevents most of the warranty disputes we see.
Number 6: life at a temperature
L70 at 25 °C is a laboratory number. In a sealed 15 mm profile the strip runs 55–65 °C and reaches L70 in roughly half the rated hours. Specify the case temperature the installation will actually produce, and ask for L80 if the space is difficult to service.
A specification template
COB LED strip, 480 chips/m, 24 V, 12 W/m, 1,100 lm/m minimum at CRI 90 with R9 ≥ 50, 3000 K ±100 K, SDCM ≤ 3 across the whole order from one production lot, 25 mm cut length, IP20 in a ventilated profile, L80 50,000 h at 45 °C case, 5 m reels with JST SM connectors, bin code on the reel label.
Every clause in that sentence is measurable, and every clause can be verified against a shipment. For the stocked configurations that meet it, see COB LED strip; for volume projects where cost per lumen dominates, the trade-offs are in COB vs SMD.
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.