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Director of Photography

Cinematography 101: Lumen and Lux

Writer's picture: Esra TanrıverdiEsra Tanrıverdi

Updated: Jan 25

When I was just 20 years old, I attended a cinematography seminar on short films. The first question posed by a cinematographer from the industry was, "Does anyone here know what lux and lumen are?" Of course, none of us had even heard of these terms. By the time we moved on to lux, lumen, candela, light brightness, light intensity, and luminous flux, my mind was completely scrambled.

Not understanding much of the explanation, I immediately started researching available Turkish resources (and this was a time when Google and YouTube didn’t have nearly as much content on cinematography as they do now). I ended up purchasing Cinematography by Blain Brown and Lighting for Film and Television by Gerald Millerson.

But I wish I hadn’t. Unfortunately, I found the translations to be quite poor, especially Blain Brown's book. In their effort to localize the technical terms, the translations made the material even more complex than it originally was.

Years later, while thinking about where to start writing for my blog, lux and lumen came to mind. So, I hope I can briefly and clearly explain the meaning of these two terms and provide some examples of where they are used.



lümen ve lux lumen nedir mum ışığı 1 metredeki lux değeri
1 lux, 1 metrekareye 1 lümen ışığın düştüğü yoğunluğu ifade eder.


Lumen (lm):

Lumen measures the total amount of light emitted by a lamp or light source. In essence, it indicates how bright a light source is.


A higher lumen value corresponds to a brighter light source. For example, the sun at midday under clear skies has a lumen value of approximately 100,000 lumens, while the average lumen value of a single candle is around 12 lumens.


Lux (lx):

Lux measures the amount of light falling on a surface. It is a unit used to calculate the intensity of light hitting a given area. One lux equals one lumen per square meter.


In other words, lux indicates the distribution and intensity of light in a given area. Lux values decrease as the distance from the light source increases, following the inverse square law.


This means that when the distance is doubled, the light intensity is reduced to one-fourth. For instance, if the lux value is 100 at a distance of 1 meter, it will drop to 25 lux at 2 meters.



Lux değeri nasıl hesaplanır formül

Ters kare yasası nedir belli bir mesafede ışığın parlaklığı ne kadar azalır
Ters Kare Yasası

Where Do We Need to Calculate Lumen and Lux?

For example, when deciding which light to use. Imagine we’re about to shoot a scene in a studio with a ceiling height of approximately 5 meters. I want to expose the shot at ISO 400 and T4. Which light source should I choose?


The Classic Analog Film Rule: 4-4-4 Rule

Let’s start with a straightforward, old-school rule that’s easy to remember:


4-4-4 Rule: At 400 ASA (ISO), you need 400 lux to expose at T4 (for 24fps, 1/48 shutter angle).


*Technically, this should be 500 lux, but the 100-lux difference accounts for only a 0.3 T-stop adjustment. Since it’s easier to recall and calculate on set, people use 400 lux for this rule.


Determining Minimum Lumens


While there are formulas to calculate the required lumens based on various factors, many people (myself included) find these formulas complex. Thankfully, in today’s world, we don’t always have to rely on manual calculations. Instead, we can use apps or websites like Arri’s Photometric Calculator or check the photometric data provided by the light source manufacturer to determine the required brightness.


Example with the Arri L5-C

Let’s say you’re considering using an Arri L5-C light source for this setup. According to its photometric data:


At a 5-meter distance in FLOOD mode (where the light is spread out), it delivers 136 lux.

However, in SPOT mode (where the beam is focused), it delivers 1182 lux.

If you plan to diffuse the light for a broader coverage, the 136 lux won’t be sufficient to achieve proper exposure at T4. But in SPOT mode, with a lux value of 1182, the light intensity is more than adequate.


To achieve the correct exposure in SPOT mode, you would need to either dim the light or use ND filters to reduce the brightness.



Arri photometrics lux ışık parlaklığı hesaplama

Beam Diameter and Lux


The beam diameter (the width of the light circle at a given distance) also affects the lux value. When the light is more focused (in SPOT mode), the intensity increases as the light covers a smaller area. Conversely, in FLOOD mode, the light spreads out, decreasing its intensity on the surface.



Lux değeri spot flood olduğunda değişimi
An example of how the beam diameter affects the light intensity (lux)

Fresnel lamba flood spot halinde lux değeri değişimi
, Here’s an illustration of a Fresnel light. As shown in the Spot mode, the beam diameter decreases from 60 degrees to 10 degrees, which increases the light intensity.  

Of course, we can also give an example by thinking about this situation in reverse. Let’s say we’re doing an outdoor shoot and we have a light meter in hand. We’re filming a speaker, and we want to find the correct exposure settings for the scene. When we point the light meter at the speaker’s face, we measure the light intensity at that spot. This tells us which T-stop we need to use for the shot. Let’s say our light meter shows 800 lux.


Now, let’s recall the 4-4-4 rule. With 800 lux (which is 2 times more light than 400 lux), it means the shot is 1 stop overexposed. In this case, I can place an ND3 filter on my camera. This will reduce the light hitting my lens by 1 stop and allow me to achieve proper exposure.


Some Useful Websites:

ARRI Photometrics App: You can access it for both Android and iOS by clicking these links. Android   IOS


An example website you can use to calculate how much lux you need: toolstud.io




güneş gün batımı sokak ışığı lux değerleri tablosu

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