LED power calculator
A 5 metre strip at 14.4 W per metre is 72 W, and its driver should be rated at least 20% above that, so 90 W or more. Running a driver at its exact rating shortens its life sharply, and the strip itself dims measurably along its length if fed from one end only. For runs over five metres, feed from both ends or split into separate runs.
LED energy is total watts times hours divided by a thousand. A 48 W run for five hours a day uses 87.6 kWh a year: about £25 at 28p per unit. Size the driver at least 20% above the strip wattage.
How to work out LED power
The headline saving from LED is real but often overstated in one direction and understated in another. A 10 W LED replacing a 60 W incandescent genuinely cuts that fitting by 83%, but lighting is rarely the largest load in a home, so the household saving is modest. The understated part is heat: in a kitchen with twenty halogen downlights, 1,000 W of lighting was also 1,000 W of heating, which is why the room felt different afterwards.
Questions
It is printed per metre; commonly 4.8, 9.6 or 14.4 W/m. Multiply by the length for the total.
At least 20% above the total strip wattage. Running a driver at exactly its rating shortens its life.
Voltage drop in the strip copper. Feed from both ends, or split into runs of five metres or less.
Per fitting, dramatically. As a share of a household bill, modest: heating, hot water and cooking usually dominate.
Less, but not proportionally on all dimmers. PWM dimming scales close to linearly; some analogue dimmers do not.