How to use a Light Meter

In this article and video I’ll show you how to use a light meter. Just a warning: You’ll find many kinds of advice on this subject, and some may well be contrary to what I’m saying, so take this as my way to use a light meter. If it doesn’t work out, find some other way.

First, here’s the video on how to use a light meter:

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Three ways to use a Light Meter

There are three ways to use an incident light meter:

For exposure

If you point the meter directly at the camera, the dome reads the collective light from all the sources hitting it within 180 degrees. This is used to get an exposure for camera.

Because modern cameras have different settings and presets, you can’t rely on this completely for consistency. I do not recommend this method for exposure, and I do not use this.

What are the alternatives? I find the following solutions are far more accurate and fast (in order of precision):

  • Waveform
  • In-camera meter
  • False color
  • Zebras

For Contrast Levels

If you point the dome directly at the source, you will mostly read the light from it. Because the dome is three-dimensional, if there are other light sources they might all spill some light onto the measurements.

Which is okay, because your actors are going to be lit the same way. Light builds up.

I primarily use this system to measure contrast levels (or contrast ratios). This is the difference between lights at different areas.

This means you’ll need to understand your camera and how it exposes. Also, you’ll need to light to a fixed aperture. Then it’s only a matter of fine-tuning the camera parameters (like ISO, gamma, color space, LUTs, etc.) to match your lighting style.

For tighter Contrast Levels or for Flat Surfaces

When you don’t want light from other sources contaminating your reading, you can retract the dome (not all meters have this option). In all other respects, it’s the same as the second method otherwise.

There’s only one advantage to retracting the dome – isolation. This is most useful in scenarios where you want to measure flat surfaces like walls or chroma keys, etc. Unlike heads or three dimensional objects, walls and backgrounds are flat.

What measurements am I taking?

I’m measuring either one of two things:

  • F-stop/T-stop, EV or
  • Lux (Foot candles if that’s what you prefer)

The former allows me to accurately calculate the contrast levels quickly. E.g., if at one place the reading is f/2.8 and at another place its f/4, I know the contrast ratio is two stops to one. I also use EV because it’s easier to calculate.

I use Lux to measure light directly so I know how much bang for the buck I’m getting from my fixtures. I believe once you’re experienced you can judge this easily by eye, and you’ll eventually know roughly what kind of fixture and modification you’ll need for every scenario.

To know more about lux and footcandles, read this article.

Advantages of an Incident Meter

Here are the key advantages of an incident meter:

  • The characteristics of the camera do not matter, as you can vary them to suit your lighting style
  • The lenses don’t matter, and you can swap lenses as long as you maintain a single T-stop
  • The reflectance of surfaces, skin tones, etc., don’t matter. Everything just “falls into place”.
  • The position of the camera or camera movement really doesn’t matter, so you can light an area quickly and the director can change his/her mind.
  • Exercise!

Together with a calibrated production monitor, you can do wonders with a light meter. Many great cinematographers actually stop using light meters because they can see light in ways most of us can’t. Don’t assume that means you don’t need a light meter. You do, at least till you are a master of light.

For more information on what a light meter is, the different types of meters or whether you need one, check out What is a Light Meter and do you need one for Video?

I hope you’ve found this article and video useful.

Exclusive Bonus: Download my free swipe file on how to shoot night scenes well (PDF file optimized for mobiles and tablets).