Light is the heart and soul of capturing a beautiful image. How we manipulate light and expose for it is partly artistic and partly technical. The latter utilizes specific techniques to accurately capture the image we envision. The term foot candle may raise a few questions. What is a foot candle exactly? What is the comparison to other light measurement units like lumens or lux? Let’s demystify the foot candle and take a look at how it applies to real world cinematography and photography.
What is a foot candle of light?
Foot candle definition
The term foot candle is one of the oldest light measurement terms, but it has evolved and adapted to be used by modern photographers and cinematographers. Let’s take a look at the foot candle definition to understand how it is used today.
FOOT CANDLE DEFINITION
What is a foot candle of light?
A foot candle is a term used to measure the amount of light that falls on a surface that is 1 foot away from a singular candle. The term “foot candle,” sometimes abbreviated as FC, originated from a time when candles were the main light source available. Since then, the term is still widely used in photography and cinematography to measure a light’s intensity on a subject.
Terms used to measure light:
- Foot candle
What is a foot candle used for?
Foot candle vs lux
Before we dive into how to measure a one foot candle, you’ll need to understand the difference between it and a lux. FCs and lux are both commonly used when measuring light in filmmaking and photography.
Just like feet and meters are both used to measure length, foot candles and lux are both used to measure how much light is emitted onto a surface.
The main difference between the two is that an FC is a measurement used in the imperial measurement system whereas a lux is used in the metric system.
To better understand the two as well as learn why foot candles to lumens is not a conversion used in filmmaking, check out this video lesson by Aputure below.
Note the conversions to lux: one foot candle = 10.76 lux. This is typically rounded to around 10 lux for convenient use and easier lux to foot candles conversions. Every light in the industry will have specifications listed in both lux and FCs.
Here is a lux and foot candle chart that shows the required amount of light for different spaces. This chart will also give you a better idea of the conversion between the two.
Use of one term or the other will typically depend on the set you are working on and where you are in the world. Some sets may use the imperial measurement system while others use the metric system.
How to calculate foot candles
How to measure foot candles
Learning how to calculate foot candles is as easy using a light meter. Because FCs are always consistent, they are great to utilize when location scouting and testing lights on a set.
Foot candles and lux do not change even when your camera settings do. This will help you determine your camera settings like aperture and ISO as well as how much light you need. Check out this video on using light meters to measure FCs to understand how and why they are so useful.
As they noted in the video, it’s worth having foot candles, lux, and f-stops on your light meter display at the same time to monitor lighting values and your camera’s exposure. This will allow you to be effective and efficient.
To fully understand the value of FCs, go out and buy a light meter and begin testing for a shot. This will give you real world experience that will inevitably help you when you get on set.
Ultimate Guide to Aperture
Understanding FCs is crucial in understanding how light falls on a surface. To understand how to capture light, it is imperative to learn about aperture. Without a solid understanding of aperture and its effect on depth of field, it is much more difficult to capture the images you envision as a cinematographer or photographer. Learn everything about aperture in our next article.