How to calculate the energy costs of your lighting
The basic formula is simple:
Annual consumption (kWh) = number of luminaires × power per luminaire (kW) × operating hours per year
Energy costs (€) = annual consumption × electricity price per kWh
Important: with fluorescent and discharge lamps the ballast's consumption is part of the power. A “58 W tube” draws noticeably more power with a conventional ballast.
Existing: 100 luminaires × 150 W × 4,000 h = 60,000 kWh per year
LED: 100 luminaires × 80 W × 4,000 h = 32,000 kWh per year
Saving: 28,000 kWh × €0.25/kWh = €7,000 per year (around 47 %)
What do the costs of a retrofit depend on?
| Factor | Why it matters |
|---|---|
| Number and type of luminaires | Complete luminaires, modules and retrofit kits cost different amounts |
| Mounting height and access | Lifting platforms, scaffolding and barriers increase the effort |
| Working during ongoing operation | Night or weekend installation needs more planning |
| Controls and sensors | Costs extra, but saves permanently |
| Electrical installation | New cabling or circuits cost more than a one-for-one swap |
| Lighting design and commissioning | Ensures the installation meets the required values |
| Disposal | Fluorescent and discharge lamps have to be disposed of properly |
As a manufacturer with our own production in Germany we are competitively priced. We prepare a reliable quotation after a site survey – for example as part of our lighting audit.
When has LED paid for itself?
The payback period is the investment divided by the annual saving. The longer the operating hours and the less efficient the old installation, the faster it is. Figures from our projects:
| Project | Saving | Payback |
|---|---|---|
| Carl Spaeter, Hamburg | 89 % (LED + light management) | 19.1 months |
| Furniture store car park | 68 % | 19 months |
| Modern office building | 61 % | 22 months |
| Manufacturer of storage supplies | 56 % | 23 months |
| Carl Spaeter Südwest, Karlsruhe | 74 % | 23.6 months |
| F. Hackländer, Kaufungen | 76 % | 25 months |
| Electronics manufacturing, Saxony-Anhalt | 79,4 % | 28.6 months |
| Club Raffelberg | 54 % | 34 months |
| Rehberghalle in Roßdorf | 49,9 % | 39.2 months |
The figures come from the respective project reports and are not a general savings promise. They do show, however, the order of magnitude of retrofits in industry, logistics, offices and sport.
Cheap to buy or cheap to run?
Over the life of a lighting installation, energy costs usually make up the largest share of total cost – not the purchase price. So it is worth looking at:
- Luminous efficacy (lm/W): how much light per watt comes out of the luminaire?
- Service life and lumen maintenance: how much light does the luminaire still deliver after 50,000 or 100,000 hours? More in the guide LED service life.
- Replaceable drivers: if a driver fails, the whole luminaire does not have to be replaced.
- Warranty: On the Series 18 Blackline for example at least 84 months.
Sensors: saving more with the same luminaire
After the LED retrofit a residual consumption remains. Presence and daylight control reduce it further, because light only shines where and as brightly as it is needed. Our LED savings calculator typically assumes a 50 % saving from sensors on the remaining LED consumption and adapts the value to usage and the number of employees. More in the guide Presence detectors and light control.
Funding and tax aspects
There are changing funding programmes for energy efficiency measures in companies and municipalities at federal and state level. Because conditions change frequently and applications usually have to be submitted before the contract is awarded, check the current situation before the project starts, for example with your energy consultant or tax adviser.
Frequently asked questions
What does converting to LED cost per luminaire?
That depends on whether you replace complete luminaires or modernise existing fittings with LED modules, how high they are mounted and whether sensors are added. A reliable price comes out of a site survey.
How quickly does an LED retrofit pay for itself?
In our case studies the payback periods were between 19 and 39 months. Long operating hours and inefficient old installations shorten the payback.
How do I calculate the energy costs of my lighting?
Number of luminaires × power in kW × operating hours per year gives the consumption in kWh. Multiplied by the electricity price you get the annual energy costs. With old luminaires, include the ballast's consumption.
Is LED worthwhile even with few operating hours?
The payback then takes longer. Often there are other reasons, though: replacement lamps are becoming scarce, maintenance falls and light quality improves. The savings calculator shows you the order of magnitude.
