LED energy savings & carbon calculator
Size the opportunity before you tender it.
A free calculator for commercial, industrial and public-sector lighting upgrades. Enter what you run now and what you would replace it with — annual energy cost saving, payback period and carbon (CO₂e) avoided update as you type. No form, no email gate on the numbers.
What this is for
First-pass sizing for commercial, industrial and carbon-reduction lighting projects.
It uses energy and tariff only — no maintenance, controls, daylight or occupancy gains, and no allowance for tariff changes. Real projects usually land differently once fittings are surveyed. That's what the audit is for.
Start from a typical setup
Step 1
Your inputs
Running hours are applied across 365 days a year. If your site runs a shift pattern, use average daily hours.
Step 2
Indicative results
Annual electricity — before vs after
| Current annual consumption | 63,510 kWh |
| Consumption after LED | 24,090 kWh |
| Reduction in lighting energy | 62% |
| Saving over 5 years | £55,188 |
| Carbon avoided over 5 years | 40.8 tCO₂e |
Indicative only. Figures are modelled from the inputs above and are not a quotation, a survey result or a guarantee of performance.
Take these figures with you
Nothing is stored and nothing is sent. Copy or download your own numbers, or carry them into an audit request so you don't retype them.
From estimate to evidence
Get site-specific numbers your finance team can sign off.
The Lighting Decision Audit surveys and counts every fitting, models controls, daylight and occupancy gains properly, and produces a written recommendation you can take to procurement.
Method
Every figure on this page, and how it was arrived at.
How the calculation works
Annual consumption is fittings × watts × hours × 365 ÷ 1,000. The difference between current and LED consumption is the kWh saved.
Saving is kWh saved × your tariff. Payback is project cost ÷ annual saving. Carbon avoided is kWh saved × 0.207 kgCO₂e, converted to tonnes.
What it leaves out
Maintenance and relamping savings, controls and dimming, daylight and occupancy profiles, standby losses, and any change in tariff or grid intensity over the life of the scheme.
It also assumes like-for-like fitting counts. Good LED design often needs fewer fittings, which changes both cost and saving. Every exclusion is conservative — the audited case is normally better, not worse.
Carbon factor
0.207 kgCO₂e per kWh, the UK grid electricity factor used here for consistency across sites.
If you report under a specific framework — SECR, ESOS, GHG Protocol scope 2 — tell us which and we will use the factor your reporting requires.
Questions
Common questions about lighting savings calculations.
How do you calculate LED lighting energy savings?
Multiply the number of fittings by the wattage of each fitting, then by the hours in use per day and 365 days, and divide by 1,000 to get annual kWh. Do this for the current fittings and the proposed LED fittings — the difference is the energy saved. Multiply that by your electricity rate for the annual cost saving.
What is a typical payback period for a commercial LED upgrade?
Most commercial and industrial upgrades fall between one and four years on energy alone. Long-hours sites — warehouses, car parks, 24-hour operations — sit at the short end because every watt removed is running for more hours. Adding maintenance savings and lighting controls usually shortens payback further.
Which carbon factor should I use for electricity in the UK?
This calculator uses 0.207 kgCO₂e per kWh for UK grid electricity, which keeps results consistent when comparing sites. If you report under SECR, ESOS or the GHG Protocol you may be required to use a specific published factor for the reporting year, in which case use that instead.
Are these figures accurate enough for a business case?
They are a first-pass estimate, suitable for deciding whether a project is worth investigating. They are not a quotation or a survey result. A business case going to finance needs surveyed fitting counts, verified run hours and modelled control gains — that is what the Lighting Decision Audit produces.
Does the calculator include savings from lighting controls?
No. It compares wattage against wattage only. Presence detection, daylight dimming and scene control typically add a further 20 to 50 per cent on top of the wattage reduction, depending on the space and how it is occupied. Excluding them keeps the estimate conservative.
What about maintenance and relamping savings?
Also excluded. On estates still running fluorescent, metal halide or halogen, the labour and materials cost of relamping is often a material part of the real business case — particularly where access equipment is needed. It is left out here because it varies too much between sites to estimate blind.
I don't know the exact wattage of my current fittings. Can I still use it?
Yes. Use the nearest common rating and treat the output as a range rather than a figure. A twin 58 W fluorescent batten draws roughly 110 to 120 W including control gear; a 400 W metal halide high bay draws around 450 W. If the answer looks worth pursuing at a rough wattage, a survey will confirm it.
Do I have to give you my details to see the results?
No. The numbers update as you type, nothing is stored, and nothing is sent. Contact details are only needed if you want site-specific figures from an audit.