Luminous efficacy: the 200 lm/W luminaire explained

Luminous efficacy, expressed in lumens per watt (lm/W), measures the quantity of light produced for each watt consumed. Reaching 200 lm/W means obtaining a lot of light with very little energy. This article explains what this figure covers, why it has become a central criterion for professionals, and why it becomes decisive on photovoltaic installations where every watt counts double.

What is the luminous efficacy of a luminaire?

Luminous efficacy is the ratio between the luminous flux emitted (in lumens) and the electrical power drawn (in watts). A 200 lm/W luminaire therefore produces 200 lumens for 1 watt consumed. To put the orders of magnitude in context: old incandescent lamps peaked at around 10 to 15 lm/W, fluorescent lamps at around 60 to 100 lm/W. Standard LEDs now commonly reach 100 to 150 lm/W, the best products exceeding 200 lm/W.

There is a physical limit: for usable white light, manufacturers estimate the theoretical limit of efficacy at around 250 to 300 lm/W (the absolute limit for monochromatic green light at 555 nm being 683 lm/W). Reaching 200 lm/W at the level of the complete luminaire, and not just the bare LED chip, therefore places a product at the top of the current performance spectrum.

Beware of the distinction: the efficacy of the LED chip (bare component) is distinguished from that of the complete luminaire (with driver, optics, thermal losses). It is the latter, more demanding, that counts in the real calculation of a project.

Why aim for high luminous efficacy?

For a lighting manager, luminous efficacy translates directly into savings. For the same illuminance (the same lux on the area to be lit), a more efficient luminaire consumes fewer watts. Over an installation of several dozen or hundreds of light points operating thousands of hours a year, the difference between 130 lm/W and 200 lm/W represents a very significant reduction in consumption.

The benefits add up: a lower electricity bill, less heat given off (therefore less thermal stress and often a better lifetime), and sometimes a reduction in subscribed power. High efficacy is fully in line with the promise of LED technology capable of greatly reducing consumption compared with earlier technologies.

The decisive case of photovoltaics: every watt counts double

It is on solar installations that luminous efficacy takes on its full dimension. Autonomous photovoltaic lighting must produce its own energy via a solar panel and store it in a battery. All the energy available at night has first been captured, converted and stored during the day · a journey that is costly at every stage.

Consequence: on a solar installation, every watt saved at the luminaire lightens the whole chain. A more efficient luminaire makes it possible to:

reduce the size of the solar panel needed to recharge the battery;
reduce the capacity of the battery, a major item of cost and bulk;
improve autonomy and performance during days with little sun;
lighten the structure (column, fixing) and make installation easier.

In other words, in solar, gaining lm/W does not just reduce consumption: it directly determines the sizing and the overall cost of the installation. That is why luminous efficacy is a priority criterion for any solar lighting project. We develop this in our article on solar public lighting and its autonomy.

Examples of high-efficacy Rexylum ranges

Performance in lm/W is at the heart of the Rexylum ranges. The GALAXY HP, 170 lm/W linear luminaire, illustrates this high level of efficacy on a linear product designed for demanding professional uses. This efficacy is found in several references in the range, where optimisation of the driver, the optics and heat dissipation makes it possible to get the best out of current LED components.

For solar-powered projects, the Rexylum solar range brings together suitable solutions, where high luminous efficacy plays its full role as a lever on autonomy and sizing.

Luminous efficacy and illuminance level: do not confuse them

A frequent confusion is to equate luminous efficacy with illuminance level. They are two distinct notions. Illuminance (in lux) describes the quantity of light received on the area to be lit; it depends on the actual need (a workshop, an office, a pitch do not require the same levels). Luminous efficacy (in lm/W), for its part, describes the way the luminaire turns electricity into light. For the same illuminance target, a more efficient luminaire will reach the target with less installed power.

In practice, reasoning only in watts is misleading: a "100 W" floodlight says nothing about the light produced until its efficacy is known. Two floodlights of the same power can emit very different fluxes. That is why the right reflex is to compare luminaires at equivalent useful luminous flux, and then look at how many watts each consumes to deliver it. High efficacy then makes it possible to reduce the number of light points or the unit power, while respecting the required levels and the uniformity (U0) expected on the area.

A lever for energy sufficiency

Beyond the individual gain, luminous efficacy is part of a wider approach of energy sufficiency, expected of companies and local authorities alike. Reducing the installed power of a lighting installation means reducing consumption, but also lightening the needs for electrical infrastructure and reducing the carbon footprint associated with use. In commercial or industrial buildings operating continuously, high efficacy is one of the most profitable levers of a renovation, because it acts on the most recurrent item of expenditure: the energy consumed every hour of operation.

How to read a data sheet without being misled

Several precautions are needed when reading a value in lm/W. Check that it is indeed the efficacy of the complete luminaire and not of the chip alone. Make sure that the stated flux is the flux actually emitted by the luminaire (and not the flux leaving the LEDs before optical losses). Also check the associated colour temperature and CRI: pushing a very high CRI tends to reduce efficacy slightly, and vice versa. Finally, efficacy must always be considered alongside lifetime (L70/L80) and the quality of the driver, which guarantee lasting performance.

To go further on this last point, see our guide to assessing the reliability of LED lighting, as well as our overview of the evolution of LED technology that has made these levels of efficacy possible.

Efficacy and control: a winning combination

High luminous efficacy combines ideally with control systems. Presence detection, dimming, use of daylight: these devices reduce consumption further by lighting only where and when necessary. A 200 lm/W luminaire controlled intelligently combines both levers of savings. To go further, see our savings through intelligent lighting control.

FAQ

What does 200 lm/W mean in practice?

It means that the luminaire produces 200 lumens of light for every watt of electricity consumed. It is a very high level of efficacy: for the same illuminance, it consumes significantly less than a product at 130 or 150 lm/W.

Why is luminous efficacy so important in solar?

Because the energy for solar lighting is produced and stored locally. The more efficient the luminaire, the more the size of the panel and battery can be reduced, autonomy improved and the overall cost of the installation lowered.

What is the theoretical limit of LED luminous efficacy?

For usable white light, manufacturers estimate the theoretical limit at around 250 to 300 lm/W. The absolute physical limit, for monochromatic green light at 555 nm, is 683 lm/W.

Does the stated efficacy refer to the chip or the luminaire?

Both exist, and this is a frequent source of confusion. For a project, only the efficacy of the complete luminaire counts (driver, optics and thermal losses included), which is always more demanding than that of the bare chip.

Need a photometric study?

The audit and the photometric study are the work of a lighting design office: we recommend the expertise of the Luminance Consulting agency, the lighting design office that contributes to developing our ranges of luminaires based on an in-depth analysis of the needs of the most demanding customers. Luminance carries out the audit of your installation, the DIALux study and the compliance check. Rexylum, for its part, designs and supplies the prescribed luminaires and lighting solutions: for the choice of equipment, contact us.