Lumen - Unit of Luminous Flux

In a lamp, electrical energy is converted into radiant energy and emitted. Only a portion of that radiation is visible light; the rest is heat (infrared).
The total amount of visible light that a lamp emits in all directions is expressed in lumens. Only visible light counts, so the measurement takes into account the sensitivity of the human eye.

Let's compare a lamp to a water tap.

The amount of water flowing from the tap is the water flow rate, expressed in litres per hour. For a lamp, the amount of light flowing from the lamp is the luminous flux, expressed in lumens. Dimming the lamp is equivalent to turning off the tap, while increasing the lamp's brightness is similar to opening the tap further. 

Some examples: 

• A classic 60 Watt incandescent bulb had a luminous flux of 720 lumens.
• A 58 Watt T8 fluorescent lamp has a luminous flux of 5000 lumens. That's almost 7 times more light than an incandescent bulb, with roughly the same power.
• The latest LED lighting fixtures from ETAP, such as the E826/2NLD, have a luminous flux of 10000 lumens at 60 Watts. That's 14 times more light for the same power as a classic incandescent bulb.

Lux - Unit of Illuminance

The number of lux indicates how much light falls on a surface, expressed in lumens per square metre. This light can come from anywhere: a lamp, sunlight coming in through a window, reflections on walls, and so on.

To extend our water analogy, illuminance in lux can be compared to the amount of water reaching a specific spot on the ground, expressed in litres/m² per hour.

Some examples:

There are guidelines for illuminance in a work environment. For instance, general office lighting should reach 500 lux.

• A dark street with lamp posts: 5 to 15 lux
• Workshops: 150 to 500 lux
• Desks: 500 to 750 lux
• On the operating table: 10,000 lux
• Outdoors on a sunny day: 10,000 to 100,000 lux

Lighting Study

How do you find the right lighting fixtures with the appropriate lumen output for your project to achieve the desired lux level? Let ETAP support you with a lighting study.

In the example below, you can see a lighting study using four U7 luminaires with a luminous flux of 4550 lumens to achieve an illuminance of 596 lux on the work surface.  

In a lighting study, we guide you in selecting a tailored lighting solution based on your needs and compliance with standards. We assist you step by step in choosing the right luminaires and light control systems and create a detailed plan for your entire building, for every room. We outline escape routes for your emergency lighting.

We can also provide a visual presentation of the proposed lighting concept. A financial analysis, including operating costs and payback periods, is also possible.

ETAP has a range of sample studies for various reference spaces: individual offices, corridors, classrooms, and more. This way, you can compare different solutions and make a more focused and informed choice quickly.

It all starts with a good conversation!

Hassle free lighting