Light Meters 101: Why You Should Use One for Video Projects
Despite modern innovations, a dedicated light meter is still the best way to ensure consistent and high-quality results on your video projects.
Top image via Shutterstock
When exposing your scene, you have countless options — from simply eyeballing the visuals on your monitor to using your camera’s histogram or zebra stripes. But there is no denying that light meters are far and away the most accurate — and specific — way to measure exposure.
Unfortunately, many in-camera exposure options will not always give you specific enough information to make exposure adjustments with. For instance, your histogram may show that you have a hot spot in your image, but you won’t necessarily know where that hotspot is coming from. It essentially gives you an average readout from your sensor (which can be helpful and is certainly better than using nothing), but doesn’t give you the full picture of what’s really going on in your shot.
Image via Shutterstock
A light meter, on the other hand, can be used to gain exposure information on various points within your frame quickly and easily. While you can use a light meter in spot mode (which works in a similar way to your camera’s built-in light meter), many DPs like to shoot in incident mode. When shooting with an incident light meter, you can simply hold the meter in front of your talent’s face and point it at camera.
It will effectively gather the amount of light hitting your talent and let you know what your exposure settings should be based on the amount of light. If you were to use a light meter in spot mode, you would point it at your subject from the camera POV, and it would be taking a reading based on the amount of reflected light from your subject.
Both incident and spot metering can be useful in different scenarios, but for the purpose of this post, we will focus on incident metering.
Using Incident Metering
To properly meter your subjects using an incident meter, you’ll first want to input the exposure information that you already have. Assuming you are shooting at 24p, you can set your shutter speed on the meter to 1/50 and your ISO level to whatever the native ISO of your camera is — let’s say, 800.
When you take a reading of your subject, since you’ve already locked in your shutter speed and ISO value, the meter will give you an f-stop reading that represents the aperture value you need to hit in order to achieve perfect exposure. If you’re shooting on a bright day, the reading might be something high — like f16, which can be problematic if you want to shoot wide open and achieve shallow DOF.
In a situation like this, you might choose to use your light meter in a different way. For example, you might choose to also lock in an f-stop value of f/2.8 and let your meter tell you how many stops you will overexpose your talent when using those settings. If you’re five stops over, you can simply use ND filters to cut the five stops of light without having to adjust exposure settings in camera.
Image via stillmotion
This is just one basic example of how a light meter can be used, but there really are countless uses for one on any set. Many DPs like to use meters to understand contrast ratios, or they’ll meter their lights directly in order to understand exactly how much light is being generated by each individual source.
Regardless of how you choose to use it, there’s no question that the light meter is a fundamental tool that can not be replaced with any of your in-camera exposure tools. You may not need to use one, but you will inevitably get better quality — and more consistent — results when you do.
The following video from stillmotion explains some of the fundamentals of metering, and is a great watch for those interested in purchasing a light meter.
Do you use a light meter on your film set? Share in the comments below.