Five different things are called “efficiency,” and they differ from one another by tens of percent. Anyone who compares a net system value against a chip value is not comparing two luminaires, but two measurement methods.
We apply 172 lm/W net, measured at the complete luminaire with driver losses included. Below is what the five values mean, what a difference in lm/W on a site costs in terms of energy, and the five questions to check a specification.
A chip value at room temperature without driver loss is 20 to 40% higher than what the same fixture mounted on a pole delivers in July. Both figures may be expressed in “lm/W.” Therefore, always ask whether the specification refers to the complete fixture, including the driver, and at what temperature the measurement was taken.
From the LED chip to the square meter on your premises, light is lost along the way. Each of these five values measures a different part of that chain, and only the last two are about your energy bill.
A calculation example: the same container terminal of 24,000 m² at the same 50 lux, with the same beam shape and the same result on the ground. The only difference is the luminaire efficiency: 172 lm/W net versus 120 lm/W net.
Assumptions: 4,000 operating hours per year with twilight switching, €0.248 per kWh excluding VAT, 65% of the emitted lumens reach the site. This is an example, not a project quote: your operating hours and your kWh price determine the amount.
On the energy bill, year after year. But also on the investment: lower power often means a lighter power supply, thinner cables, and sometimes one less circuit. On a site with long cable routes, that is a significant cost item.
And it affects the tax side. The generic EIA code for facilities in existing commercial buildings stipulates a payback period of between 5 and 25 years. Efficiency and operating hours are precisely the two figures that determine where you land within that window.
Note the counterintuitive aspect: if the payback period is under five years, the investment falls outside that code, and under an energy-saving obligation, the measure may actually be mandatory.
For the DarkLicht series, we list the net efficiency for each model. For the floodlights, the luminous flux and power are listed on the datasheet, and you can calculate the efficiency yourself using those values.
The datasheet shows the efficiency per model, without having to download a form. We calculate free of charge what power an installation on your site requires in a lighting calculation; for the corresponding masts and cable routes, everything is set light masts and high masts.
These five questions eliminate most apples-to-oranges comparisons. If the answer is not on the datasheet, that in itself is an answer.
Honestly: a few percent difference in lm/W is negligible compared to the four choices below. We gladly sell luminaires, but this is where the real savings are.
The percentages are orders of magnitude from our own projects and not a promise: what it yields for you depends on your current installation, your operating hours, and the use of the site.
Why more lumens does not mean more light on the ground, and how much actually lands on the site.
How to read a lifespan statement, and why a number without an LB code means nothing.
What the codes guarantee, and the five things they do not cover.
All subjects together are on subsidy and knowledge base.
If you want to know what the difference would be on your own property, a light calculation with a power comparison is faster than an explanation. We provide these free of charge.
Lumens per watt: the luminous flux emitted by a luminaire, divided by the power it consumes. The higher it is, the less energy you need for the same amount of light. The pitfall is that five different figures are called this, ranging from the LED chip to the complete luminaire.
Net luminous flux is measured for the complete fixture, with the power consumption including the driver. Gross efficiency accounts only for the LED module. The difference is typically 10 to 15%. We use 172 lm/W net for the DarkLicht series and compare net values only.
Usually because that is the chip value, measured at the LED module at a favorable temperature and without driver loss. That is not untrue, but it is a different figure than what the luminaire delivers on a pole. Therefore, ask whether the specification concerns the complete luminaire, including driver, and at what temperature it was measured.
It does affect energy consumption, but it’s rarely the biggest factor. A difference of a few percent in net lm/W between two luminaires is outweighed by the choices made at the installation level: maintaining no more lux than necessary and providing a dimming profile for nighttime hours can easily save 30 to 50%. Furthermore, a luminaire with slightly lower lm/W but better optics may actually require less power, because more light is directed onto the target area.
Power in kW × operating hours per year = kWh, and kWh × your kWh price = the cost. For an outdoor area, we calculate with 4,000 operating hours with a twilight switch and €0.248 per kWh excluding VAT; for a sports field, with 500 operating hours and €0.30 including VAT. Do not mix those two calculation bases.
The efficiency decreases as the LED junction temperature rises, and that rises with the ambient temperature and poor heat dissipation. Therefore, the thermal design of a fixture is just as crucial as the LED itself, and that is why a specification includes the temperature at which it was measured.
There is an energy label for light sources, but professional outdoor luminaires are compared in practice on net lm/W and the power demanded by the installation. For a site project, the latter is the figure that counts; a label class says nothing about how much light lands on your site.
Indirect. The generic code for facilities in or near existing commercial buildings sets a payback period of at least 5 and a maximum of 25 years. Return and operating hours determine where you land within that window. If the investment pays for itself faster than five years, it falls outside that code, and in the case of an energy-saving obligation, the measure may then be mandatory.
That follows from the light level. In our calculation examples, both a terminal at 50 lux and a sports field at 200 lux come out to around 0.009 W per m² per lux. That is a rule of thumb from our own two examples and not a standard. If an offer is well above that at the same light level, it is an indication that light is spilling outside the surface.
In the projects where we’ve made replacements, the measured savings range from 68 to 80% in lighting consumption. Most of these savings come from replacing the old light source; control systems and the proper light level account for the rest. Your specific savings will depend on your current lighting setup and your operating hours.
Capacity old and new, operating hours, kWh and euro per year, including the assumptions. That is the same justification you need for an EIA notification or a subsidy application. Free of charge, and an answer from an engineer within one working day.