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LED driver sizing
The 80 % rule, the misleading rated power of CCT strips, calculating for spotlights and where to put the driver in the structure.
The 80 % rule – no exceptions
A driver must not be run at full capacity. A load over 80 % raises the temperature, cuts the lifetime from 50 000 hours to under 20 000 hours and is a common reason for drivers failing early inside the ceiling.
Driver = strip power ÷ 0.8
180 W strip load → 180 / 0.8 = 225 W → choose a 250 W driver
In practice: living room 5 × 4 m, light cove on all walls
Perimeter 18 m, but the door and window interrupt it – 15 m of strip. Single colour 14.4 W/m: 15 × 14.4 = 216 W → 216 / 0.8 = 270 W → 300 W driver, or two 150 W if you want two control groups. The same strip as a CCT version: actual power draw 10.3 W/m → 15 × 10.3 = 155 W → 155 / 0.8 = 193 W → 200 W driver. Calculated from the rated power, the CCT driver would be oversized at 300 W – €60-80 wasted.
Single-colour strip – the simplest case
The calculation for a single-colour strip is straightforward: metres × W/m = total power. Total power ÷ 0.8 = minimum driver size.
| Strip | Length | Total power | Min. driver |
|---|---|---|---|
| 7.2 W/m | 10 m | 72 W | 90 W → 100 W |
| 14.4 W/m | 10 m | 144 W | 180 W → 200 W |
| 14.4 W/m | 18 m | 259 W | 324 W → 360 W |
| 22 W/m | 10 m | 220 W | 275 W → 300 W |
CCT strip – misleading rated power
A CCT strip has two LED circuits: warm white (WW) and cool white (CW). The rated power is given as the sum of both – for example 14.4 W/m means 2 × 7.2 W/m. Since only one circuit is fully active at a time, the actual power draw is about 70 % of the rated power.
Spotlights and panels are rated by actual consumption. LED strips are not. This is an established but misleading practice in the industry.
✗ Wrong – rated power
10 m × 14.4 W/m = 144 W
144 / 0.8 = 180 W driver
The driver is oversized
✓ Right – actual power
10 m × 10.3 W/m = 103 W
103 / 0.8 = 129 W → 150 W driver
Req. value from the table
Actual power table for CCT strips
Always use the Req. (W/m) column when sizing the driver – not the rated power.
| Strip | Rated power | WW+CW | Req. W/m | Driver / 10 m |
|---|---|---|---|---|
| SOLO TUNNELMA CCT | 3.6 W/m | 2.2+2.2 | 2.9 | 50 W |
| SOLO TUNNELMA CCT | 7.2 W/m | 4.1+4.1 | 5.5 | 75 W |
| HELMI TUNNELMA CCT | 7.2 W/m | 3.4+3.4 | 4.5 | 75 W |
| SOLO TUNNELMA CCT | 14.4 W/m | 7.7+7.7 | 10.3 | 150 W |
| HELMI TUNNELMA CCT | 14.4 W/m | 6.0+6.0 | 8.0 | 100 W |
| HELMI TUNNELMA CCT | 22 W/m | 11.8+11.8 | 15.7 | 200 W |
| SOLO TUNNELMA CCT | 30 W/m | 15.6+15.6 | 20.8 | 250 W |
| NEON CCT | 14.4 W/m | 7.9+7.9 | 10.6 | 150 W |
Driver / 10 m = Req. × 10 ÷ 0.8, rounded up to the next standard size.
Spotlights and panels – actual consumption directly
Spotlights and panels are rated by actual consumption. A 9 W CCT spotlight uses 9 W, not 18 W.
| 9 W CCT spotlights | Total power | Driver |
|---|---|---|
| 2 spotlights | 18 W | 30 W |
| 3-4 spotlights | 27-36 W | 50 W |
| 5-6 spotlights | 45-54 W | 75 W |
| 7-8 spotlights | 63-72 W | 100 W |
| 9-12 spotlights | 81-108 W | 150 W |
| 13-16 spotlights | 117-144 W | 200 W |
Placing the driver in the structure
- Profile shelf: the driver on the same shelf as the LED profile – no access hatch, directly at hand. Needs a 60 × 57 mm opening.
- Access hatch: the driver inside the plasterboard, with its own hatch of at least 300 × 300 mm. Required if the driver is inside the ceiling.
- Adjacent cabinet: cable through the structure into a cabinet – neater, no hatch needed in the same room.
- In another room: a feed-through in the wall or ceiling. The driver completely hidden, no heat issues in the living space.
LED drivers → LedStore
LED drivers → LedStore
Frequently asked questions
How big a driver is needed?
The strip’s actual power draw multiplied by the metres, plus 20 % headroom. 17 W/m × 8 m = 136 W, so a 165 W driver. For CCT strips use the actual power draw, which is lower than the rated power.
Why leave 20 % headroom in the driver?
A driver running at full load heats up, and heat shortens its lifetime quickly. At 80 % load the driver stays cool and lasts years longer.
What is the difference between a dimmable and a standard driver?
A dimmable driver can reduce power steplessly and without flicker. A standard driver with a dimmer causes humming and flicker at the lowest settings.
Can the driver be installed in a plasterboard bulkhead?
Not advisable. The driver is the part that fails first, and a plastered-in driver means opening the ceiling. Put it behind an access hatch or on top of a cabinet.
Which voltage, 12 or 24 volts?
24 V. Voltage drop is half as large, so the strip can be longer and the light stays even. 12 V is only justified in solar panel systems.