How to Use a Light Meter to Get Correct Exposure in Your Photos

What a light meter does and why you need one

A light meter measures the amount of light falling on or reflecting from your subject, then tells you which combination of shutter speed, aperture, and ISO will give you a properly exposed photograph. Your camera has a built-in meter, but a handheld meter gives you more control and accuracy, especially in tricky lighting where the camera's meter can be fooled.

The meter reads light and converts it to an exposure value (EV) — a single number that represents the brightness of the scene. Once you know the EV, you can dial in your camera settings to match it. This is particularly useful when you're shooting film, working with studio flash, or photographing scenes with extreme contrast (a white wall next to a dark shadow, for example).

A handheld meter is also faster than chimping — checking your camera's LCD screen between shots — because you get your answer before you even raise the camera to your eye.

Key Takeaways

• A light meter reads brightness and gives you an exposure value, which you then translate into shutter speed, aperture, and ISO settings on your camera.
• Point the meter's dome or flat diffuser at the light source (for incident metering) or at your subject (for reflected metering), press the button, and read the number.
• Incident metering (measuring light falling on the subject) is more reliable than reflected metering (measuring light bouncing off the subject) in most situations.
• Once you have an exposure value, you can choose any combination of settings that adds up to that value — faster shutter with wider aperture, or slower shutter with narrower aperture.
• Handheld meters are most useful for film photography, studio work, and scenes with extreme contrast where your camera's built-in meter struggles.

Incident metering versus reflected metering

A light meter can work in two ways: incident or reflected. Incident metering measures the light falling onto your subject. You point the meter's dome (or flat diffuser) toward the light source — the sun, a studio flash, a window — and take a reading. This tells you how much light is actually hitting the scene.

Reflected metering measures light bouncing off your subject. You point the meter at the subject itself, as if you were aiming a camera at it. This tells you how much light the subject is reflecting back.

Incident metering is more reliable for general photography because it ignores how dark or light your subject is. A white wall and a black wall in the same sunlight will give you the same incident reading, which is correct — they're both in the same light. Reflected metering would tell you the white wall is brighter, which is true, but would lead you to underexpose the black wall.

Most handheld meters default to incident mode. If yours has a switch or button to toggle between modes, check your manual to confirm which is which.

How to take an incident meter reading

Stand where your subject will be (or as close as you can get without blocking the light). Hold the meter so the dome faces the main light source — the sun, a window, a studio light. Press the button or trigger. The meter will display a number, usually shown as an EV or as a combination of shutter speed and aperture at a specific ISO.

If your meter shows "EV 14," that's the exposure value. If it shows "1/125 at f/5.6 (ISO 100)," that's one valid combination of settings — but you can use any other combination that adds up to the same exposure. Faster shutter speed means you need a wider aperture to compensate, and vice versa.

In studio work, take a reading from each light separately if you're using multiple flashes. Point the meter at each light in turn, note the reading, and adjust your flash power or distance until the readings match what you want. For outdoor work, one reading from the main light direction is usually enough.

Translating meter readings into camera settings

Once you have an exposure value, you need to set your camera. If your meter displays the reading as a number (like EV 14), you'll need to convert it using a chart or your meter's built-in calculator dial. Most modern meters show the reading as actual settings: "1/250 at f/8 (ISO 400)."

Those settings are a suggestion, not a requirement. You can trade shutter speed for aperture in either direction. If you want more depth of field, use a narrower aperture (f/16) and a slower shutter speed (1/30) instead. If you want to freeze motion, use a faster shutter speed (1/1000) and a wider aperture (f/2.8). As long as the combination adds up to the same exposure, your photo will be properly lit.

Set your camera's ISO first, because that anchors everything else. Then choose your aperture based on the depth of field you want, and your shutter speed based on whether you need to freeze motion or allow blur. The meter reading tells you whether those choices will work together to expose the scene correctly.

When to use incident metering in the field

Incident metering works best when you can physically reach your subject or stand very close to it. In portrait work, take a reading from the subject's face, pointing the dome toward the main light. In landscape photography, take a reading from the foreground where your subject will be standing, or from the sky if the sky is your main subject.

If you can't reach your subject — photographing a distant mountain, a bird in a tree, or a stage performer — use reflected metering instead. Point the meter at the subject itself and take a reading. The result will be less reliable because it depends on how much light the subject reflects, but it's better than guessing.

In high-contrast scenes (bright sun and deep shadows), take separate incident readings from the lit side and the shadow side. If the readings differ by more than two stops, you'll have to choose which area to expose for correctly and let the other fall into shadow or blow out. The meter can't solve that problem, but it tells you the problem exists before you shoot.

Using a light meter with flash and studio lighting

A handheld meter is especially useful in the studio because it lets you balance multiple flash units without taking test shots. Set your camera to manual mode and set the shutter speed to your camera's flash sync speed (usually 1/200 or 1/250 — check your manual). Set ISO to 100 or whatever you prefer.

Fire a test flash and take an incident meter reading from where your subject will stand, pointing the dome toward the main light. Adjust the flash power up or down until the meter shows the aperture you want. Repeat for fill lights and other flashes, adjusting each one until the readings match or create the ratio you're aiming for.

This workflow is much faster than shooting a frame, checking the LCD, adjusting, and shooting again. You dial in the lighting before the subject arrives.

Common mistakes and how to avoid them

The most common mistake is pointing the meter in the wrong direction. For incident metering, the dome must face the light source, not the subject. If you point it at the subject, you're accidentally doing reflected metering, and the reading will be wrong.

Another mistake is taking a reading and then moving to a different location without re-reading. Light changes as you move — a spot in shadow will read differently than a spot in sun. If you move, take a new reading.

In studio work, some photographers forget to account for the distance between the meter and the subject. If you take a reading from three feet away but your subject will be ten feet away, the light will be dimmer by the time it reaches them. For studio work, take the reading as close to the subject position as possible.

Finally, don't assume the meter is always right. If a reading seems wrong — if the meter says the scene is very bright but it looks dim to your eye — trust your eye and bracket your shots (take multiple exposures at different settings). The meter is a tool, not a may provide.

Frequently Asked Questions

Do I need a handheld meter if my camera has a built-in meter?

No, but a handheld meter gives you more control and is faster in studio work. Your camera's built-in meter works fine for most situations. A handheld meter is most useful if you shoot film, work with studio flash, or often encounter high-contrast scenes where your camera's meter struggles.

What's the difference between spot metering and incident metering?

Spot metering is a type of reflected metering — your camera reads a small area of the scene. Incident metering measures light falling on the subject. Incident is generally more reliable because it ignores how dark or light the subject is.

Can I use a light meter app on my phone instead of a handheld meter?

Phone apps can estimate exposure, but they're less accurate than a real meter because phones don't have a proper diffuser dome. For casual photography they're fine. For film work or studio lighting, a real meter is worth the investment.

What if my meter and my camera's meter give different readings?

They may be measuring different things. Your camera might be using spot metering on a bright area while your handheld meter is reading the whole scene. Take a reading with both pointed in the same direction. If they still differ, trust the handheld meter — it's designed to be more accurate.

Do I need to change my meter reading if I change ISO?

No. The exposure value stays the same. If you change ISO from 100 to 400, you're making the sensor more sensitive, so you need to close the aperture or speed up the shutter by two stops. The meter reading itself doesn't change — only your camera settings do.