Quick answer: For a grid-connected street light, estimate electricity use by multiplying its actual electrical input in kilowatts by the hours it operates. For a fixture drawing 100 W for 10 hours, the arithmetic is 0.1 kW × 10 h = 1.0 kWh for that night. For dimming, calculate each operating period separately and add the results. Use the luminaire’s documented input or a suitable measurement—not its lumen output—and label all assumed hours as assumptions.
This method estimates energy, not brightness, lighting quality or a guaranteed electricity bill. A project calculation should state which equipment is included, how the operating schedule was chosen, and whether the input power is rated, measured or assumed.
The basic street-light kWh formula
Energy (kWh) = actual input power (W) ÷ 1,000 × operating time (h). A kilowatt-hour is the energy used by a one-kilowatt load running for one hour. The formula works for one fixture, a group of fixtures or a defined circuit, provided the power and time refer to the same boundary.
For a fleet, first calculate the energy for each fixture type or operating group, then add those values. If every light has the same input and schedule, the shorter form is: fixture kWh × number of fixtures. Do not multiply by the number of poles if a pole carries a different number or type of luminaires than assumed.
Use actual input watts, not light output
Watts describe electrical input; lumens describe emitted light. A lumen value cannot be substituted into an electricity calculation. Start with the luminaire schedule, manufacturer data sheet or a documented measurement at the agreed operating condition. Check whether the figure is for the complete luminaire or only an LED module, and whether a control device or other auxiliary load is included.
For a project comparison, keep the basis consistent: compare complete luminaires, the same number of operating hours and the same set of included controls. If measured power is used, record the instrument, test point and control state so another reviewer can understand the result.
Calculate a simple nightly example
The figures below are hypothetical arithmetic examples only. They are not Jieyao product ratings, recommended schedules or claims about a particular road.
| Assumed actual input | Assumed operating time | Calculation | Energy for one night |
|---|---|---|---|
| 60 W | 10 h | 0.060 kW × 10 h | 0.60 kWh |
| 100 W | 10 h | 0.100 kW × 10 h | 1.00 kWh |
| 150 W | 11 h | 0.150 kW × 11 h | 1.65 kWh |
These examples show why wattage alone is not enough: the operating schedule changes the energy result. For an annual estimate, multiply the nightly value by the number of operating nights, or use month-by-month schedules if the hours vary seasonally. A simple 365-night multiplier is an assumption, not a universal operating calendar.
Model dimming or multiple operating scenes
When the light changes state during the night, split the schedule into periods. For each period, multiply the actual input power in that state by its duration, then add the period results. Use the input wattage measured or documented for each state where possible. A dimming command expressed as a percentage does not necessarily mean the electrical input falls by precisely the same percentage.
For example, a hypothetical fixture drawing 80 W for five hours and 40 W for seven hours uses (0.080 × 5) + (0.040 × 7) = 0.68 kWh in that night. This arithmetic example does not describe a Jieyao control profile or product.
Before comparing schedules, confirm the switching times, time zone or controller basis, daylight-saving treatment where relevant, and what happens during overrides or communication loss. The approved operating plan—not an assumed generic dimming curve—should define the calculation.
Scale from one light to a road or network
Group the inventory into like-for-like sets: fixture input, number of fixtures, operating hours and control schedule. Calculate one set, multiply by its verified quantity, and sum the groups. Keep a location or circuit identifier so the estimate can be checked against the asset schedule and later utility data.
For mixed systems, separate the boundaries. A grid-connected luminaire calculation is not the same as a solar street-light energy balance. Solar systems require a separate accounting of load, battery, charging input, conversion losses and control assumptions; do not apply the grid formula to panel output or battery capacity as if they were interchangeable.
Estimate energy cost without inventing a tariff
Multiply calculated kWh by the applicable energy rate to estimate the energy-charge component. Use the rate and billing period supplied by the utility or project owner. A final bill may also include fixed charges, demand charges, taxes or other items that are not captured by a simple kWh multiplication. Tariffs vary by location and contract, so an article should not imply one universal street-light price.
For a comparison between two proposals, show both the kWh method and the tariff assumption. Do not present a lower-wattage fixture as guaranteed to reduce a project’s total cost unless the lighting performance, operating schedule, controls, maintenance and complete tariff basis have also been evaluated.
Inputs to record in a project worksheet
| Input | What to record | Why it matters |
|---|---|---|
| Fixture input power | Value, source and whether rated or measured | Defines the electrical load used in the calculation |
| Quantity and grouping | Fixture type, circuit or location and count | Prevents unlike equipment from being combined invisibly |
| Operating schedule | Hours, seasons, switching basis and exceptions | Energy changes with run time and control state |
| Dimming states | Power and duration for each state, if documented | A command percentage alone may not define electrical input |
| Included equipment | Luminaire, controller and other auxiliary loads | Makes the system boundary explicit |
| Tariff basis | Rate, period and excluded bill components | Separates an energy estimate from the complete invoice |
Common calculation mistakes
- Using lumens instead of electrical input watts.
- Mixing LED-module power with complete-luminaire input.
- Applying one operating schedule to fixtures with different controls or seasonal hours.
- Assuming a dimming percentage equals the same percentage reduction in input watts.
- Multiplying by pole count without checking the number and type of luminaires per pole.
- Calling a kWh estimate a complete electricity bill while excluding tariff and demand-charge terms.
- Comparing energy use without confirming that both options meet the project’s lighting criteria.
Frequently asked questions
How much electricity does a street light use per night?
It depends on the light’s actual input power and operating time. Multiply kilowatts by hours; use separate periods for multiple control states. Without those inputs, there is no single reliable number for every street light.
Is a 100 W street light using 100 kWh?
No. A 100 W load is 0.1 kW. If it operates for 10 hours, the arithmetic result is 1 kWh. That example assumes a constant 100 W input for the full period.
Can I calculate electricity use from lumens?
No. Lumens measure light output; kWh measures electrical energy over time. Use input-power data for the electrical calculation and evaluate lumens and photometric distribution separately for lighting performance.
Does dimming reduce electricity use in direct proportion to the setting?
Do not assume a one-to-one relationship. Use input-power data for each operating state or a documented project method; a dimming command alone may not specify electrical watts.
How do I estimate a monthly electricity bill?
Multiply the period’s calculated kWh by the applicable energy rate, then add or separately account for other billing items according to the local tariff. Ask the utility or project owner for the relevant rate and charge structure.
For a roadway project, keep the energy worksheet separate from the electrical-current and circuit review. See the existing lighting-system current requirements guide for that different question, and the dimming-scene commissioning checklist for scene verification and handover. For a project quotation, send Jieyao the project brief; product configuration and input-power data must be confirmed for the specific model.
