Candela vs. Lux vs. Lumen: Illuminating the Differences & How To Calculate Them

Candela vs. Lux vs. Lumen

When it comes to getting the right lighting for a system or some other sort of application, there is no doubt that understanding what to measure at every turn is incredibly important. Several things come together to determine the efficiency of your lighting, and each of these will have its own particular metric. 

In this article, we’ll look at three metrics that tend to be mentioned a lot when measuring the efficiency of lighting – candela, lux, and lumens.  

Candela (cd): How We Measure Luminous Intensity

A Defining Luminous Intensity 

For a start, we have candela – a metric that helps to measure luminous intensity. 

If you’re unaware, luminous intensity is a term that measures just how much light is gotten from a specific direction, all based on the unit of solid angle. Or, in much simpler times, the term measures the brightness of a light source when it is consumed by the human eye.  

It’s a common fact that the human eye can be very sensitive. And this is especially true for specific light wavelengths – especially those in the green-yellow area. With luminous intensity, we’re able to take a specific wavelength of light and measure just how bright it is, especially to the human eye. 

Some people tend to mistake luminous intensity for brightness. But, just as we have candela vs lumen, there are several differences between brightness and luminous intensity. Being able to mark these distinctions will be very important. 

How Candela Measures Luminous Intensity

To get luminous intensity, we use this formula: 

Luminous Intensity (cd)= Luminous Flux (lm)/Solid Angle (steradian)

This brings us to the unit of measurement – the candela. Abbreviated as cd, candela is the unit that has been approved by the International System of Units for capturing luminous intensity. And, here are a few things you might want to note about it: 

A Focus On Monochrome Light: To begin, this definition focuses primarily on light with a singular frequency. For luminous intensity, this frequency tends to be about 540 terahertz – which will place it in the region between green and yellow. 

Linkage With Radiant Intensity: In some cases, we can see that when we measure candela, we get something related to radiant intensity for the particular light. Since radiant intensity measures light power in all directions, candela can break that down into a single direction. 

Divide Your Number By Angles: For you to get candela, refer back to our formula. It is important to divide the luminous flux by the unit of solid angle, which is expressed in steradians (sr)

Lux (lx): The Metric For Measuring Illuminance

car light

A Definition & Importance of Illuminance 

Next, let’s look into lux to see if there’s a candela to lux pipeline or if there are links between the two metrics. 

To understand lux, we need to be familiar with the concept of illuminance. Here, you have a measure of how much light can fall on a surface per unit area. Essentially, illuminance looks at the luminous flux of a light source but takes that per a singular unit area.

There are several reasons why it is important to measure and be aware of illuminance. Some of these include: 

Improving Overall Performance & Visibility 

Understanding illuminance will go a long way in helping you to optimize visibility across the board. Lighting is needed in different forms, and each of them will need its visibility levels. With illuminance, you know if you’re measuring up.

Making Sure An Environment Is Safe

Proper knowledge of illuminance is also needed to ensure that you can optimize safety in public spaces as much as possible. If lighting doesn’t have enough illuminance, then it might not be ideal for protecting anyone. 

Designers Need Illuminance Too

Interestingly, illuminance also plays a very important role in aesthetics and design. In these spaces, it’s not uncommon to see professionals lighting different areas to create a particular ambiance. So, they need to be aware of illuminance and how it helps them. 

Creating Efficient Lighting Fixtures

An understanding of illuminance will come in handy when you need to design energy-efficient lighting systems. Thus can help to reduce energy bills and optimize consumption as much as possible. 

Artists Using Illuminance For Content 

Whether it’s filmmaking or photography, understanding and manipulating illuminance will go a long way in ensuring that you can achieve the right visual effect for your content. 

The Calculation & Formula For Lux

For you to measure illuminance, you need to express it in terms of lux (lx). Most times, this measurement is done with the use of a lux meter – or, an illuminance meter, if you will. 

However, there is also a mathematical approach to calculating lux or illuminance. This is: 

E = Luminous flux (lm)/ Area (m2)


  • E is the illuminance, which you get in lux
  • Luminous flux measures how much visible light a source generates 
  • The area is the particular surface area where the light source shines its light on

If you’ll be making use of the lux meter, however, all you have to do is: 

  • Choose the right meter. Make sure it can measure your chosen illuminance range, too
  • Calibrate the meter to zero, and adjust if you have to
  • Choose where you want to measure, and hold the meter steadily in front of it
  • Take your measurement, and you can repeat this process if you need to

Lumen (lm): How It Measures Luminous Flux

We’ve spoken about luminous flux already when trying to assess a candela lux link. Now, let’s look into the metric and how lumens help us to understand it better. 

In its simplest form, luminous flux helps us to measure the amount of light that a source emits per time. It looks into the brightness of light based on human eye perception, while also because the human eye perceives different light wavelengths differently. 

Essentially, luminous flux helps us to express how much light we get from a light source, regardless of where that light is moving. As it gets higher, it means that the human eye perceives the light to be brighter. 

In general, we measure luminous flux with this formula: 

Φv = Km ⋅Φe

Based on this formula, we have the following definitions:

  • Φv is the luminous flux itself, which we will take in lumens
  • Km is the luminous efficiency function – essentially, the fact that human eyes perceive different light wavelengths differently
  • Φe is the radiant flux, which measures how much power the light source is generating

We need to note that the luminous efficiency function ensures that your reading for luminous flux considers the human eye’s sensitivity. Since the human eye gets especially sensitive to the green-yellow region, this is important to factor in. 

All in all, luminous flux comes in very handy when you need to represent a source’s light output in a way that considers human visual capabilities. And, considering that luminous flux also comes into play when you have to measure illuminance, it’s easy to see lumens vs lux vs candela links here.

Candela vs. Lux vs. Lumen: What Are The Relationships Between Them?

light chart

Now that we kind of understand the three metrics that we’re talking about, let’s see how we’re able to draw links between them. Can you convert lux to candela? Is there a way to have a candela vs lumens comparison? Let’s take a look:

The Dynamics Of Candela

So we know that candela helps to measure luminous intensity. At the same time, when you measure candela, we get the equivalent of the luminous intensity of a source that emits monochrome light with 540 terahertz in frequency and 1/683 watt per steradian in radiant intensity.

How The Lumen Works

With lumen, you have a measure of luminous flux. Now, this is where we can see a relationship between the lumen vs candela. Essentially, the relationship between them is reflected in the form of a solid angle. 

A single lumen is the same as the luminous flux generated into a unit solid angle by a light source with 1 candela in luminous intensity. So, a formula for them can be drawn as:

1 lumen = 1 candela x 1 steradian

Introducing The Lux Component 

Finally, we have lux, which shows how much the illuminance of a light source is.

Interestingly, there’s also a link between lux and lumen. This link is mostly brought about by the area over which your light is being shared. So, singular lux is pretty much equal to a lumen per one square meter. Something like this:

1 lux = 1 lumen/ 1 square meter

Generally, all of these relationships show that the candela vs lumens vs lux comparison can easily be judged and drawn. It is important to note that these comparisons depend significantly on things like light direction, the area in question, and even the major characteristics of the light source. 

And, when you’re able to get the right linkage, you should be able to incorporate a solid lighting design with a standardized way of measuring the performance of your lighting

How To Choose The Right Unit for Different Applications

light chart

Given the lux vs candela vs lumens comparisons, it can be understandably confusing if you don’t know which option to choose or are unaware of how best to look out for the right things. 

To help clear things up, here is a quick guide that can help you make the right choice for units, depending on your application:

If You’re Working On An Architectural Design

For this functionality, luminous intensity will help you get the right highlight for particular architectural features. So, you need to measure candela. 

At the same time, you’ll need to have an eye on lumens because luminous flux will help you with optimizing your general lighting. 

Installing lights In Outdoor Spaces

For outdoor lighting, both candela vs lumens comparisons can come in handy. You need luminous intensity for street lights, and luminous flux will also help to optimize things like floodlights and more. So, both metrics come into play.

Fixing Lights In Your Workplace

For workplace lighting, illuminance will help to ensure that you have enough light on surfaces and to handle tasks. And, you will need luminous flux for overall lighting levels that will be run across the workspace.

General Content Creation

For filmmaking and photography, luminous intensity helps you to properly focus lighting on your object. Plus, with luminous flux, you can also ensure that you have the right brightness levels for every single scene.

Growing Plants & Herbs

You want to have the right amount of luminous flux to ensure that your light intensity is optimal. At the same time, you consider illuminance if you want to determine the right level of light intensity that gets to the plant canopy.


Luminance, luminous intensity, and luminous flux have become especially popular in different types of lighting applications. Regardless of what you’re trying to achieve, finding the balance between them and knowing what you need will definitely be important. 

At NSE LED Cloud, we’re committed to helping you understand these lines. Reach out to us if you have any questions.

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