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This post was most recently updated on January 8th, 2023

The more experience you get in the world of photography, the more factors you’ll be bringing into play to get the best results possible. A lot of these elements are impossible to master without the help of specific equipment.

One of the most common pieces of equipment used by photographers is the light meter, which works as a light measuring device. They’re a vital tool for any professional shoot.

But how do they work? And what is their purpose? It can be tricky to find these answers out, especially if you are new to photography.

But luckily for you, that is where we come in! The following article will break down all you might need to know about the light meter, and all of the ways the device is most frequently used.

Light Meter Explained

The purpose of the light meter is quite simply to measure light. There are two types of light meter: the incident light meter and the reflective light meter.

Incident Light Meter

The incident light meter measures the light that’s actually on the subject, which helps cameras to focus on the subject regardless of whether the background is dark or light.

To use the incident light meter, the photographer will hold the meter near their subject. The lighting is collected in the round white zone (referred to as the lumisphere) to achieve the correct measurement.

To read the exposure meter, the user will be shown the shutter speed, the aperture, and the ISO settings that will be required for optimal exposure.

Reflective Light Meter

The reflective light meter, on the other hand, essentially does the opposite, measuring the light that’s being reflected by the subject.

All modern digital cameras come with built-in reflective light meters. It tends to be very accurate, with the odd exception of when there are sudden changes in light absorption.

For example, a light piece of clothing might look perfectly fine with certain settings, but a darker piece of clothing could be underexposed with those same settings.

How Do Built-In Meters Work?

How Do Built-In Meters Work

So, digital cameras use a built-in reflective light meter to determine the exposure of a scene. But how does this work?

With most digital cameras, the light meter tends to be always activated (as long as the camera is on), or it will be activated when the user half-presses the shutter button.

The camera first takes into account the light that’s reflecting off the subject via the lens (TTL). Next, the camera’s exposure meter will let you know whether your image requires more light (underexposed), or requires less light (overexposed).

The meter system of the lens will also allow the camera to determine the amount of exposure it needs to provide when the user has a flash setup.

Generally, a light meter is crucial if you’re trying to achieve optimal exposure. If the lighting of your photographs looks the way you intended, it could end up saving you a lot of time that you would’ve otherwise needed to spend editing the photos.

Evaluative, Multi, Or Matrix Metering

Matrix metering, multi-metering, or evaluative metering is a process through which the photographer can acquire optimal exposure for the whole scene that they’re shooting.

A camera utilizing this setting will break the scene up into separate sections, and use these sections to work out the average optimum exposure for the scene as a whole. This will take into account factors such as shadows and highlights, ensuring that everything is properly balanced.

This tends to be the kind of light meter most commonly used because it’s suitable for almost every kind of subject or scene. It’d be rare that a landscape photographer, for example, wouldn’t be using matrix metering.

Dynamic Range

The term ‘dynamic range’ refers to the range between the darkest black of your image, and the lightest white. The middle of this range is 18% gray, and that’s the point that is always used as a device’s benchmark when it comes to producing optimal exposure.

The dynamic range is also known as the latitude, and the majority of modern digital cameras will have either seven or eight f-stops of latitude, meaning there will be roughly four f-stops above the 18% gray, and four f-stops below it.

The reason it’s so vital to understand this rule is that, with every device, there will be appreciable limits when it comes to the dynamic range of an image sensor.

This means that, in some cases, the optimal shot will be a little overexposed, or a little underexposed. You shouldn’t be following the light meter’s guidance to a tee- at least not for every shot.

Gray Cards

Because 18% gray is the center of a camera’s dynamic range, you can purchase 18% gray cards that will allow you to obtain your device’s exact dynamic range.

All you need to do to use a gray card is head to the exposure settings, and hold one of your gray cards up to the lens, so it’s covering the entire frame.

The reason 18% gray functions as the dynamic range’s exact center is fairly complicated, but ultimately, it’s just the right amount of neutral to optimize highlights and shadows, and the balance of both.

Can You Use Your Phone As A Light Meter?

It’s usually possible to use your smartphone as a light meter. Modern phones tend to have one lens at the very least (although the number of lenses on high-end phones continues to grow), as well as a light sensor.

There are several light meter applications available to download to your phone. These applications will use your phone’s hardware to read the light.


A light meter can be crucial for measuring the right amount of exposure for any given shot, which is why light meters are almost always built into modern digital cameras.

But just because 18% gray is the benchmark neutral tone, this doesn’t mean you should be sticking with it for every shot.

When you’re setting the exposure, aim to expose the highlights, more than just sticking with the default 18% gray settings. There are other ways you can manually determine the best exposure, but these will come with practice.