Three numbers, not one
Every LED cabinet datasheet lists maximum power, average power, and sometimes standby. Maximum is all pixels at full white at maximum brightness, which almost never happens. Average is roughly 35 to 45 percent of maximum for normal video content. Standby is what you pay when the screen is dark but the controller is still powered.
The worked example
A 30 square metre outdoor P4 wall, 6500 nits rated, running at 6000 nits during the day and 1200 nits at night. Cabinet max is 800 W per square metre. Average at full brightness is about 300 W per square metre. At 6000 nits (92 percent of rated) that is roughly 280 W. At 1200 nits it drops to under 70 W.
The bill
| Period | Hours | Load | kWh |
|---|---|---|---|
| Day, 6000 nits | 10 | 8.4 kW | 84 |
| Night, 1200 nits | 8 | 2.1 kW | 17 |
| Standby | 6 | 0.3 kW | 2 |
| Daily total | 24 | 103 |
Where the estimate goes wrong
Three things push real consumption above the calculation. First, HVAC: every kilowatt-hour of screen power becomes heat inside the enclosure, and removing it costs more. Second, power supply efficiency: at 88 percent efficiency you lose another 12 percent. Third, high ambient temperature raises LED forward voltage slightly, so a 45 degree cabinet draws a little more than a 25 degree one.
What to ask the supplier
Ask for average power at 70 percent brightness, not maximum. Ask for the power supply efficiency curve. Ask whether the cabinet has a smart power mode that dims unused regions. Those three answers turn a guess into a number you can put in front of a client's facilities manager.