A kilowatt-hour is the energy unit used for lighting running-cost estimates.
A kilowatt-hour, or kWh, is power used over time. Lighting cost estimates combine kWh with user-entered cents per kWh.
Technical meaning
A kilowatt-hour is an energy quantity: one kilowatt of load operating for one hour.
Lighting kWh is driven by connected load, number of fittings, operating hours, operating days and any control schedule that changes run time or output.
Calculation use
Annual kWh equals watts divided by 1,000, multiplied by fitting count, hours per day and days per year.
Annual cost is the kWh figure multiplied by the entered cents per kWh and divided by 100.
Not the same as
kWh is not brightness. It says how much energy the lighting group uses, not how much light reaches the task plane.
kWh is not a tariff forecast. The estimate should carry the entered rate and the date or bill basis used for that rate.
Australian context
Australian lighting energy notes should state the assumed cents per kWh, operating schedule and lighting group so the annual figure can be checked later.
Examples
Example
Value
Planning note
100 W for 10 hours
1 kWh
Power converted to kilowatts, then multiplied by time.
12 x 10 W for 8 h/day
0.96 kWh/day
Daily energy before annual days and tariff are applied.