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Differences between luminous flux and luminous intensity

20 Feb 2024 // by Àfrica Sabé

There are lighting parameters that seem complex, words that are often used in the lighting design or engineering sector, but which, on the other hand, escape the everyday vocabulary of the space designer.

 

Designers are generally lazy about technique, but it is interesting for us to know some concepts that can help us to define our project and its lighting atmosphere. Luminous flux is one of the most basic and forgotten.

 

What is luminous flux?

 

Let's analyse word by word, we all understand that a FLOW is the movement of a fluid, but we are talking about light, that's why it has the complement LUMINOUS and in these apparently technical words the magic of light is discovered.

 

Light is a radiation, we call it visible radiation, because it allows us to see, an intangible material that we cannot touch, it surrounds us and is always in movement from the moment it originates, it bounces from surface to surface so that we can see what surrounds us.

 

In short, luminous flux is the amount of light emitted by a luminaire, it is the amount of energy that comes out of the light source converted into visible radiation and makes it possible for us to see what is around us.

 

If we google Luminous flux we will get millions of very technical definitions and mathematical formulas that we are not going to analyse now, the important thing is that we understand that the luminous flux is the amount of light radiated by the luminaire we are analysing, observing or even designing if it is the case.

 

 

 

How is luminous flux measured? 

 

In order to be able to compare luminaires it is interesting that we have a unit of measurement. Luminous flux is measured in Lumens (abbreviated lm) and lumens give us the amount of luminosity that a light source generates.

 

We commonly compare luminaires or light sources according to power, how many watts does this bulb have (consume)? How many times have you heard/asked this question? But it is more interesting to know how many lumens does this bulb emit?

 

I pose this question to you: What is going to define your project: the energy consumed by the projected luminaires (watts) or the light they emit (lumens)? What do you think if from today onwards we start talking about lumens and not watts?

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How does knowing the luminous flux help us in a project?

 

When we are designing a space, we have many parameters on the table: qualities, materials, finishes, execution budget, programme requirements, specific regulations, construction timings, etc. 

 

Knowing the luminous flux of the luminaires helps us to pre-dimension the lighting in order to be able to match the atmosphere we want to transmit with the finished space from the early stages of the design.

 

Is luminous intensity the same as luminous flux?

 

As I wrote at the beginning of this article, there are many technical concepts that it is interesting to go through one by one, but luminous intensity is closely linked to luminous flux, so we are going to see how they complement each other. 

 

It is already clear that the luminous flux is the light emitted by the luminaire in question, but how is this luminous flux distributed in the space? 

 

The luminaires we install in our projects do not normally radiate light uniformly in all directions, we select them according to how they direct or distribute the light in our space depending on the atmosphere we are looking to create. 

 

Luminous intensity is measured in candelas (abbreviated cd) and is the measure that tells us how much light a light source emits in a particular direction.

 

 

Luminous flux helps us to understand the amount of light in a space in general, while luminous intensity is the parameter we use to calculate the exact levels of light hitting each surface. Both concepts are the basis for most numerical lighting calculations.

 

We hope that with this article you will lose your fear of the technical concepts of lighting and enter into the magic of its design. 

 

At Faro Barcelona we have a great team of experts who can help you select the luminous flux that your design requires and accompany you in the product selection to make your project shine.