9.1: Measuring Light

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Christopher Clemens
Laney College, City College of San Francisco, San Francisco State University, Los Angeles City College via ASCCC Open Educational Resources Initiative (OERI)

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Measures of Light

Light intensity (the brightness of light) hitting an object is measured in Footcandles or Lux. Footcandles (fc) is commonly used in the United States but is conforming more to the rest of the world that uses Lux, which is based in the metric system. One Footcandle is equal to 10.8 Lux. When starting with lighting, you want to try to aim for 150 to 200fc, which will allow you to have some flexibility with your camera settings instead of having to open your iris completely. It is much easier to reduce light when you have too much than to increase light when you do not have enough.

Light meters

To measure the intensity of light, there are two meters that are most common in video production, the incident light meter, and the reflected light meter.

Incident Light Meter

An Incident Light Meter (See figure 9.1.1) measures the intensity of lighting hitting an object. If you have talent standing on a lit set, then you can use this light meter to measure the light hitting your talent or any other objects on the set.

Some incident light meters will show you the intensity of the light in Footcandles or Lux. Many other incident light meters measure the light hitting the sensor and they display the camera settings you need for proper exposure. To explain this further, the video below will talk about how incident light meters measure light for proper exposure.

To watch this video with Closed Captions: https://amara.org/en/videos/dzWzA1H9mzYs/info/the-light-meter-a-simple-explanation/

Reflected Light Meter

A Reflective Light Meter measures the light reflecting off of a set. Most cameras are built with a reflective light meter inside, which gives us the ability to use Zebra Stripes or a Histogram to measure the exposure.