It’s not common to see a photographer use a handheld light meter anymore. Light meters would seem to be as old-school as it gets; after all, don’t our digital cameras have meters built right inside? Yes they do, and very sophisticated meters at that. But a handheld meter can be more accurate and more versatile.

When it comes to measuring light there are two ways to go about it. First we have reflected light metering where a device measures the amount of light that is coming off of the subject and computes an exposure. Then there is incident light metering where the light coming from the light source itself is measured and then calculated into an exposure reading. Properly employed there are benefits to both methods.

Because incident meter readings are taken of the light source itself the color or reflectivity of the subject doesn’t enter into the equation. Imagine that we have three plates of fruit, one each white gray and black. If we use an incident meter and measure the light falling on the plates our camera settings will be the same no matter which plate is used in the image. If we shoot all three plates of fruit our images will accurately capture both the color of the fruit but the plates as well.

If instead we use a reflected light meter such as the one built into our digital cameras we see some results that we won’t like. Each time we swap plates in front of the lens our camera’s meters will alter the exposure values. After taking a picture of each plate in turn we are likely to see that in all three images the plates are almost the same shade of gray. Further the fruit will likely be under exposed on the white plate and over exposed on the black plate. Why would this be?

When a meter relies on reflected light, such as our built-in camera meters, the amount of light available to be measured is directly related to the color or reflectivity of the subject. In the above example the white plate reflected more light so the camera’s reflected light meter reduced the exposure. The results are under exposed fruit and a grayish plate. Conversely the black plate reflected less light so the camera’s meter increased the exposure which gave us over exposed fruit and again the plate was approaching a grayish color.

On the left an Incident Meter was used, on the right the camera’s Reflected Meter. The darker area of snow in the image on the right has unrecoverable lost detail. We can do a lot of things in Photoshop to copy in detail and texture, but isn’t it easier just to capture the image right in the first place?

This same set of results happens with any light source – sunlight, flash or studio lights. When we are metering a scene for a general exposure an incident light meter will usually give us better results.

OK, this works for an overall scene exposure setting, but what happens if our main subject is a person standing under a tree in a brightly lit meadow? We could simply walk to the person and take an incident light meter reading from under the tree. This would give us a reading taken in the same light as the subject and we would have to do this if we wanted to use our incident meter. Our other choice is to stay put, aim a reflected light meter at the subject and set our exposure from that reading. In this instance I’d choose the reflected light meter reading.

Reflected light meters are at their strongest when they are used to sample the contrast range of a scene. By sampling important areas of a scene it is possible to calculate an exposure setting that is best able to render a good image. The first two areas to sample are the darkest shadow and the brightest highlight that we want to see detail in. This range should encompass no more than eight stops*. Anything darker than our shadow sample target will be black and anything brighter than our highlight sample target will be detail-free brightness.

Once the readings are calculated into an exposure setting the image should print just the way I want it to. But here is the rub, our built-in camera meters sample an area too large to get an accurate fix. We need a very narrow sample that we can use with high accuracy. This defines a spot meter. A spot meter samples only a one-degree area of our scene. And a good spot meter can take several readings and calculate our best exposure setting on its own.

Many digital cameras have selectable meter configurations including Center Only metering (some companies call this spot metering but that’s not quite right). All of these various meter setting can be used with a little practice to get exposures that are good enough in many lighting situations.

What if we want better than “good enough”? When a photographer is ready to take a next step in image improvement purchasing a handheld light meter isn’t a bad idea. Light meters aren’t inexpensive camera accessories and a good one will carry a price tag over $250.00. However a good light meter is an asset that can last almost indefinitely.

There are several brands available but I have always had the best results with Sekonic. If the photographer feels comfortable using the camera’s built-in meter for reflected light situations then the Sekonic L-358 is a good choice. The L-358 is an incident light meter that can be used with ambient light or studio flash. However if the photographer is looking for a handheld meter that does it all then the Sekonic L-758DR is both a spot meter and an incident meter. Either way the photographer winds up with a meter that should last decades.

*I recommend an exposure range of eight stops for several reasons. First, while our eyes may be able to discern a range of up to 20 stops (depending on age) our camera image sensors can only capture between nine and 11 stops of light. Finally our LCD monitors can only show us an eight stop range and an ink-jet print about the same. As an added thought expose toward the highlight side of the scene; if the scene measures more than 8 stops in range select an exposure that favors capturing the important highlight details. Viewers are more tolerant of black shadow space compared to blown out highlights.