Last updated: 2026-07-02

Why Switching to LED Saves Money

Lighting is one of the easiest places to cut a household electricity bill. An incandescent bulb turns roughly 90% of the power it draws into heat rather than light, so most of what it costs to run is wasted. An LED producing the same brightness draws a fraction of the power. This calculator turns the wattage difference, run time, and electricity rate into concrete annual energy, cost, and CO₂ savings.

How It Works

Each bulb's savings come from the difference between its old and new wattage, multiplied by how long it runs and scaled by the number of bulbs:

where $E_s$ is the energy saved in kWh, $t_d$ is hours run per day, $d_y$ is days used per year, $n$ is the number of bulbs, $p$ is the electricity rate per kWh, and $f$ is the grid emission factor in kg CO₂ per kWh. Dividing wattage by 1000 converts watts to kilowatts so the result lands in kilowatt-hours.

Worked Example

Suppose you replace ten 60 W incandescent bulbs with 9 W LEDs, each running 5 hours a day, all year, at an electricity rate of $0.15/kWh and a grid factor of 0.4 kg CO₂/kWh.

First, the annual energy saved:

Then the cost saved:

And the CO₂ avoided:

So a modest set of ten fixtures saves about $140 a year and keeps roughly a third of a tonne of CO₂ out of the atmosphere — before counting the LEDs' far longer lifespan.

Watts vs Lumens

Old bulbs were bought by wattage because, within incandescent technology, more watts meant more light. LEDs break that link: they deliver the same brightness for far less power. Match a replacement by lumens, not watts.

Payback and Lifespan

The energy saving usually pays for the bulb within a year or two, and the LED keeps saving long after. A $3 LED replacing a 60 W bulb that runs 5 hours a day at $0.15/kWh saves about $1.40 a year, so it pays back in roughly two years. Rated LED lifetimes of 15,000–25,000 hours mean one LED often outlasts a dozen incandescents, cutting replacement cost and waste on top of the energy saving.

Choosing a Grid Emission Factor

The CO₂ figure depends on how your electricity is generated. The 2023 global average is about 0.4 kg per kWh, but grids vary widely.

If your electricity comes from a fully renewable tariff, set the factor to 0 — you still save money, but the on-grid CO₂ saving is already accounted for elsewhere.