What is Lumen? Lumen and Lux Explained

Feb 6, 2019 | Design

What is Lumen?

The official definition is: “a unit of luminous flux in the International System of Units, that is equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions.” But even we struggle to understand all this jargon andand answer questoins such as what is lumen?,  we have to call on our 20 years of lighting knowledge to explain things as simply as possinle.  So it’s more complex than this, but a quick explanation would be, lumens are light – the higher the lumens the brighter the light output. This is not to be confused with Watts which measure energy use, not brightness. For example, a 6W LED fitting has a similar number of Lumens to a 40W incandescent lamp.

All our light fittings state their approximate lumen output on the spec sheet so you can always work out how bright your space will be. The fittings are all tested in the factory to ensure there’s no lumen loss and we also conduct random testing to ensure fittings are as bright as they promise to be.  Hopefully this helps you better understand and answer the question of what is lumen? 

What is Lux?

Lux is a unit of light measurement where the area is also taken into account. 1 lux equals 1 Lumen/m2, in other words – light intensity in a specific area. While a Lumen is the amount of light coming out of a light fitting, Lux is the amount of light hitting a surface. This is especially important in offices and work areas – a general office space needs to have 300- 500 lux on the desk while areas like corridors and stairwells only need 80-100 lux. We use a Lux-meter to measure Lux on a surface but there are other ways of calculating Lux levels.

0.05–0.3 – Full moon on a clear night
50 – Dining general
80 – Office general
110 – Kitchen general
450 – Office task
500 – Kitchen task
32,000–100,000 – Direct sunlight

For this example, you need to multiply the dimensions of a kitchen task area by the lux’s needed using the above chart.  So if the example Kitchen worktop is 4m x 0.6m = 2.4m², multiplied by 500, you can work out the Lux needed is 1200.  The Lightmaster Darlek Fixed downlight produces 486lm, so you divide the lux needed by the lumens produced to know you need to install 3 Darlek downlights over the worktop to light it effectively.

lumens and lux explained

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