LED Savings Calculator
Calculate energy savings, payback period, and CO\u2082 reduction when upgrading to LED lighting
Reference Info & Formulas
Annual kWh
kWh = (W x qty x hrs x days) / 1000
Payback Period
Years = Investment / Annual Saving
CO₂ Saving
kg = kWh saved x 0.207
GU10 halogen: Replace 50W with 5W LED for 90% saving
T8 fluorescent: 5ft 58W to 22W LED tube saves 62%
Best ROI: High-hours commercial sites pay back fastest
Part L: New installs must meet 75 lm/W (dwellings)
Recommended kit
As an Amazon Associate we earn from qualifying purchases.
BAGZY Electricians Tool Bag for Men Tool Bags Heavy Duty with Laptop Compartment for 17 inch Waterproof Tools Bag Backpack With USB Port for Industrial Construction Work Storage Organization Orange
Stanley Fatmax 1-79-215 Backpack
Rexmica 12-Inch Tool Storage Organizer for Men, Heavy-duty Small Tool Bag, Multi-functional Work Tote with Thick Padded Bottom and Shoulder Strap for Electrician, Repairman, Handyman, Gardener, Black
V-TAC 10 x GU10-4.5W LED Bulbs (35W Equivalent) - 400 Lumen - GU10 LED Spot Light for Maximum Efficiency and Energy Saving - Cool White 6500K
Aigostar GU10 LED Bulbs 10 Pack, 8W Spotlight 640lm Cool White 6500K, 100° Wide Beam Angle (Equivalent to 88W), Non-Dimmable for Ceiling & Recessed Lights
10 X JCB 5w = 50w LED GU10 100deg 6500k Daylight 345 lm [Energy Class A+]
Data: UK grid CO\u2082 factor 0.207 kg/kWh (2024)
For guidance only. The responsibility for any electrical installation lies with the qualified person carrying out the work. Always verify calculations independently and apply professional judgement.
Wattage Equivalents Across Technologies
Understanding the wattage equivalents helps you select the correct LED replacement and estimate savings accurately.
LED lamps produce the same light output (lumens) at a fraction of the wattage of legacy technologies. The table below shows typical watt-for-watt replacements used in UK domestic and commercial installations.
Legacy to LED wattage equivalents
| Legacy Type | Legacy W | LED W | Saving % |
|---|---|---|---|
| GU10 Halogen | 50 | 5 | 90% |
| T8 Fluorescent (5ft) | 58 | 22 | 62% |
| T5 Fluorescent (5ft) | 35 | 18 | 49% |
| CFL (Compact Fluorescent) | 20 | 10 | 50% |
| Incandescent GLS | 100 | 12 | 88% |
| SON-T (HPS 250W) | 250 | 100 | 60% |
| Metal Halide 400W | 400 | 150 | 63% |
LED wattages are typical values; actual wattage varies by manufacturer and lumen output.
Approved Document L Efficacy Targets
Building Regulations set minimum lighting efficacy requirements that effectively mandate LED in new installations.
Approved Document L (Conservation of Fuel and Power) sets minimum luminous efficacy targets for fixed lighting. These targets apply to new builds, extensions, and major refurbishments in England and Wales.
Minimum efficacy targets (Approved Document L 2021)
HM Government, Approved Document L (2021 edition)| Building Type | Efficacy Target | Typical LED Performance |
|---|---|---|
| Dwellings (Part L1) | 75 lm/W | 80-150 lm/W |
| Non-dwellings (Part L2) | 95 lm/W | 100-170 lm/W |
Halogen (15 lm/W) and CFL (60 lm/W) cannot meet these targets. Only LED achieves the required efficacy.
When specifying lighting for a new installation, always check that the selected LED fitting meets or exceeds the relevant efficacy target. Product datasheets list efficacy in lumens per watt (lm/W).
ROI and Payback Calculation
The simple payback period tells you how many years it takes for the energy savings to cover the upfront investment. It is the primary metric used to evaluate LED upgrade projects.
Payback (years) = Total Investment / Annual Saving (\u00a3)- Total Investment
- = Cost of LED lamps plus any installation labour
- Annual Saving
- = Difference in annual electricity cost between existing and LED lighting
Simple payback method — does not account for electricity price inflation or discount rates
Commercial Sites Pay Back Faster
Domestic Quick Wins
Frequently Asked Questions
SparkyHub is a free resource built by Taro Schenker — I build websites for trade businesses too.