Lighting Energy Cost Calculator

How to use this calculator

Wattage — enter the bulb’s wattage from the packaging. Not the “equivalent” marketing number — the actual power draw. A 9W LED labelled “60W equivalent” uses 9 watts.

Hours per day — how long the bulb runs daily. Kitchen lights at 5–6 hours, bedroom lamps at 2–3 hours, outdoor security lights at 8–12 hours.

Electricity rate — your cost per kilowatt-hour (kWh). Find it on your electricity bill, usually in the range $0.10–$0.35/kWh depending on country and provider.

Number of bulbs — scale to a room or your whole house. 40 bulbs is a typical UK or US household.

The result shows daily cost, annual cost, and — when you enter both old and new bulb wattage — the annual saving and payback period on the new bulb’s purchase price.

The formulas

Everything the calculator does comes from one core equation:

Daily cost = (Watts × Hours per day) ÷ 1,000 × Rate ($/kWh)

From that, everything else follows:

A 60W incandescent at $0.13/kWh running 5 hours/day: (60 × 5) ÷ 1,000 × $0.13 = $0.039/day → $14.24/year. A 9W LED doing the same job: (9 × 5) ÷ 1,000 × $0.13 = $0.006/day → $2.13/year. Annual saving: $12.11 per bulb. At $5 for the LED vs $1 for the incandescent, payback is under four months.

Annual running cost: 10 bulbs, 5 hrs/day, $0.13/kWh

The gap between incandescent and LED is $121/year for 10 bulbs — $1,210 over 10 years. A household with 40 light sockets saves roughly $4,840 over a decade on electricity alone, before accounting for bulb replacement costs. An incandescent lasts ~1,000 hours. An LED lasts 25,000. Over the LED’s life you would have replaced an incandescent 25 times.

Lumens vs watts: matching the right replacement

Watts measure electricity consumed. Lumens measure light produced. When replacing a bulb, match by lumens — not watts. “60W equivalent” on LED packaging means approximately 800 lumens.

The 9W = 60W equivalence: A 9W LED producing 800 lumens replaces a 60W incandescent exactly. “60W LED” isn’t a thing — that wattage would produce blinding light. When packaging says “60W equivalent,” it means ~800 lumens at 8–10W. Always check the lumen rating on the box, not the wattage.

Electricity rates by country

The same LED upgrade produces very different financial returns depending on where you live.

UK and German rates are 2–3× higher than the US average. The same $5 LED that pays back in four months at US rates pays back in under two months at German rates. High-electricity-cost countries have the strongest financial case for LED upgrades.

Where the savings are biggest: room-by-room priority

Not all bulbs save equally. A bulb running 10 minutes a day and a bulb running 10 hours a day are completely different decisions.

The closet bulb is the wrong place to start. A bulb running 10 minutes a day saves $0.40/year — payback on a $5 LED is over 12 years. Outdoor security lights and kitchen fixtures running 6–10 hours daily pay back in under six weeks. Start with the highest-usage fixtures and work down.

The full LED payback over a lifetime

A single 9W LED at $5 replacing a 60W incandescent at $1, running 5 hours/day at $0.13/kWh:

• Annual electricity saving: $12.11 per bulb
• Payback on price premium: ~4 months
• LED lifespan: 25,000 hours = 13.7 years at 5 hrs/day
• Lifetime electricity saving: $166 per bulb
• Replacement bulbs avoided: 25 incandescents × $1 = $25
• Total advantage per bulb: $166 + $25 − $4 incremental cost = $187

That’s a 47:1 return on the $4 incremental investment. The numbers work everywhere except low-usage fixtures.

LED colour temperature guide

Colour temperature is measured in Kelvin (K) and determines whether light looks warm or cool. It does not affect energy consumption — a 9W bulb at 2700K uses exactly the same electricity as a 9W bulb at 5000K.

CRI (Colour Rendering Index) measures how accurately a light source renders colours. Incandescent scores ~100. Look for CRI 80+ for home use, CRI 90+ for kitchens, art display, or retail. Budget LEDs can score 70 or below — colours appear washed out and unflattering under them.

Dimmer compatibility

Not all LEDs work with dimmer switches. An incompatible combination produces flickering, buzzing, limited dimming range, or premature LED failure. Three things to check:

1. The LED must be labelled “dimmable.” Non-dimmable LEDs connected to a dimmer can be permanently damaged. The label must say it explicitly — don’t assume.

2. The dimmer switch must be LED-compatible. Old dimmers were designed for incandescent loads (resistive, high-wattage). Modern LED-compatible dimmers — usually labelled “LED/CFL” — handle low-wattage loads without flickering.

3. Minimum load requirements. Many dimmers need at least 40–60W to function smoothly. Two or three LEDs at 9W each (18–27W total) may fall below that threshold, causing flicker or uneven dimming.

The safest approach: replace the dimmer switch at the same time as the bulbs. A $15–20 LED-compatible dimmer eliminates compatibility problems. Brands like Lutron and Leviton publish compatibility lists online where you can verify your exact LED model and dimmer combination before purchasing.

Common LED myths

“LED bulbs don’t fit in old lamp fixtures.” Standard LEDs use the same E26/E27 (medium) or E12/E14 (candelabra) base as incandescents and fit directly. Some directional fixtures need specific form factors (BR30, PAR38), but LED replacements exist for all of them.

“LED light is harsh and cold compared to incandescent.” That was true of early LEDs from 2008–2012. A modern LED at 2700K is visually indistinguishable from incandescent warm light. With CRI 90+, it often renders colours more accurately.

“LEDs last forever and never need replacing.” LED lifespan is typically 15,000–25,000 hours at rated output. They don’t fail suddenly — they gradually dim. End of life is defined as 70% of original brightness (L70). Budget LEDs with poor heat sinking can fail much earlier, especially in enclosed fixtures.

“All LEDs are the same — just buy the cheapest.” Cheap LEDs frequently have low CRI (poor colour rendering), inadequate heat sinking (early failure), visible flicker at 100 Hz (causes eye strain and headaches), and poor dimmer compatibility. Energy Star-certified or brand-name LEDs cost $1–3 more but perform reliably over their rated lifespan.

Smart bulbs: when the premium is worth it

Smart LEDs (Philips Hue, LIFX, Govee) cost $15–40 each versus $5–8 for a standard LED. The electricity math doesn’t change — a 9W smart LED costs the same to run as a 9W standard LED. The question is whether the smart features justify the price premium.

The premium pays off fastest in two scenarios:

Frequently-forgotten lights. A home office LED running 8 hours instead of 5 because you forget to turn it off wastes 3 extra hours daily: 3 × 9W ÷ 1,000 × 365 × $0.13 = $1.28/year. Small, but a scheduled smart bulb eliminates it.

Outdoor security lights. Motion-triggered smart outdoor lights can reduce runtime by 60–80% compared to always-on lights. A security fixture running 12 hours/night at 15W versus 3 hours/night with motion detection saves $4.26/year per bulb — enough to recover the smart premium within 2–3 years.

For always-on or frequently-forgotten fixtures, smart bulbs pay back their premium. For lights that already get used efficiently, a standard LED is the better value.

Environmental impact

The US electricity grid emits approximately 0.386 kg of CO₂ per kWh (EPA 2023). One 60W incandescent running 5 hours/day: 60 × 5 × 365 ÷ 1,000 × 0.386 = 42.3 kg CO₂/year. One 9W LED doing the same job: 9 × 5 × 365 ÷ 1,000 × 0.386 = 6.3 kg CO₂/year. Saving: 36 kg CO₂ per bulb per year.

A household switching 40 incandescents to LEDs prevents roughly 1.44 tonnes of CO₂ per year. Over the LED’s 13.7-year lifespan, that’s nearly 20 tonnes avoided — approximately equivalent to taking one car off the road for two years.

The financial payback (months), environmental payback (immediate), and comfort improvement (better colour rendering, no flicker, no hot surfaces) all point the same direction. The only real question is which fixtures to upgrade first — and the answer is always the ones running the most hours per day.