LED vs. Incandescent Savings — kWh & Cost per Year

How This Calculator Works

We compare energy used by the original bulbs vs. LEDs for your hours and count. The difference is your annual kWh saved; multiply by your electricity price for annual bill savings. Optionally, we estimate CO₂ saved (grid intensity × kWh saved), and if you add bulb prices & lifetimes, we include annualized bulb replacement costs and a simple payback on buying LEDs now.

• kWh saved/year: (W_inc − W_LED) × hours/day × days/year × bulbs ÷ 1000
• £/$ saved/year: kWh saved × price per kWh
• Annualized bulb cost: price × (hours used per year ÷ lifetime hours)

Note: Payback treats LED purchase as upfront; incandescent “baseline” assumes you’d otherwise keep buying incandescents over time.

From Filaments to Solid-State: How Lightbulbs Evolved, Energy-Wise

The story of home lighting is really a story about squeezing more light from less power. Early incandescent lamps, popularized in the late 19th and early 20th centuries, made light by heating a filament until it glowed. They were wonderfully simple and produced warm, familiar light—but most of their energy became heat, not light. Typical household incandescents delivered roughly 10–18 lumens per watt (lm/W), meaning a 60 W bulb produced the brightness we now expect from a 9–10 W LED.

Material advances extended filament life and nudged efficiency upward. Carbon filaments gave way to tungsten, which tolerates higher temperatures. The tungsten–halogen lamp arrived later: a small quartz capsule with halogen gas that “recycles” evaporated tungsten back onto the filament. Halogens ran a bit hotter and brighter, commonly landing in the 15–25 lm/W range for household versions—better than classic incandescents but still mostly heat.

The first big energy leap in mainstream homes was the compact fluorescent lamp (CFL). Instead of heating a filament, CFLs excite a gas, which emits ultraviolet light that a phosphor coating converts into visible light. That physics change boosted efficacy several fold. Everyday CFLs typically delivered 50–70 lm/W, cutting electricity use by ~70–80% versus the incandescent bulbs they replaced. Downsides—slow warm-up in cold rooms, color rendering quirks, and a small amount of mercury—limited their long-term appeal.

The second—and decisive—leap is the light-emitting diode (LED) era. LEDs are solid-state devices: electrons pass through semiconductor layers and release photons directly. No glowing filaments, no fragile glass envelopes under vacuum, and minimal wasted heat. Early household LEDs were pricey, but rapid improvements in chips, drivers, and phosphors pushed efficacy into the 80–150+ lm/W range, with high-quality products offering excellent color, instant on, dimming options, and long service life. That’s why a 9 W LED can now replace a 60 W incandescent while matching (or exceeding) brightness and comfort.

Beyond raw efficiency, LEDs also changed lighting design. Because the light source is tiny, manufacturers can shape beams precisely, hide sources in slim fixtures, and tune color temperature from warm to daylight—or even adjust it dynamically throughout the day. Add long lifetimes (often rated 15,000–25,000 hours or more) and the maintenance math shifts: fewer replacements, less ladder time, and less waste.

Rule of thumb for quick comparisons: incandescent ≈ 60 W → LED ≈ 8–10 W; halogen ≈ 42 W → LED ≈ 6–7 W; CFL ≈ 13–15 W → LED ≈ 9–10 W for similar brightness. As LED tech keeps improving, you get the same light for even fewer watts—and often better quality, too.