Why Use a Light Meter?
When it comes to exposure metering, most photographers rely on their camera’s built-in system. While modern cameras do a decent job, they aren’t always perfect. That’s where a dedicated light meter comes in. It measures light more accurately, helping you achieve consistent exposure in different lighting conditions.
I’ve used light meters in studio and outdoor settings for years, and they’ve become an essential part of my workflow.
They remove the guesswork, particularly in tricky lighting situations where a camera’s metering can be fooled by bright or dark areas. Whether you shoot portraits, landscapes, or commercial work, understanding how to meter exposure correctly will improve your photography.
What is a Light Meter?
A light meter is a device that measures the intensity of light in a scene. It helps you determine the correct camera settings—aperture, shutter speed, and ISO—for a well-exposed image.
Unlike your camera’s built-in meter, a handheld light meter can measure incident and reflected light separately.
Incident Light Metering: Measures the light falling on the subject, offering more accurate readings unaffected by the subject’s reflectivity.
Reflected Light Metering: Measures the light bouncing off the subject. This is what your camera’s built-in meter does, but it can be skewed by very bright or dark tones.
Understanding these differences is crucial when learning how to meter exposure effectively.
Types of Light Meters and Their Uses
There are different types of light meters available, each with specific applications. Knowing which one to use will depend on your shooting conditions.
1. Handheld Light Meters
These are standalone devices that provide precise exposure readings. They are commonly used in studio photography, film production, and high-end commercial work. Many models allow for both incident and reflected metering, giving you greater control.
2. Built-In Camera Light Meters
Every digital camera has a metering system that measures reflected light. There are three main metering modes:
- Evaluative/Matrix Metering – Measures light across the entire frame and averages it out.
- Centre-Weighted Metering – Prioritises the central part of the frame for exposure calculation.
- Spot Metering – Measures light in a very small area, ideal for backlit subjects or high-contrast scenes.
While these modes are useful, they can sometimes be fooled by extreme lighting contrasts, which is where an external light meter proves valuable.
3. Smartphone Light Meter Apps
Apps like Lux Light Meter Pro or myLightMeter are handy in a pinch. They aren’t as accurate as a dedicated meter but can help when shooting film or manual photography.
How to Meter Exposure Using a Light Meter
Step 1: Set Your Camera and Light Meter to the Same Settings
Before you start, ensure that your light meter matches your camera’s settings. Input your ISO and shutter speed so the meter can calculate the correct aperture.
Step 2: Decide on Incident or Reflected Metering
For incident metering, place the light meter in front of your subject, pointing the white dome towards the camera. This measures the actual light falling on the subject.
For reflected metering, point the meter at the subject from the camera position. This helps in scenarios where you can’t get close to the subject.
Step 3: Take a Reading
Press the meter’s measure button. The screen will display the recommended aperture for the given ISO and shutter speed. Adjust your camera settings accordingly.
Step 4: Adjust Based on Creative Intent
A light meter gives a baseline exposure, but you can tweak it based on your artistic preferences. If you want a high-key image, increase exposure slightly. For dramatic shadows, underexpose slightly.
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When to Use a Light Meter
Studio Photography
In a controlled environment, using a light meter ensures consistency across multiple shots. It’s especially useful when balancing multiple light sources or achieving precise ratios between highlights and shadows.
Film Photography
Unlike digital cameras, film doesn’t offer instant feedback. Using a light meter ensures correct exposure, preventing wasted shots. Many professional film photographers rely on light meters to maintain accuracy.
High-Contrast Outdoor Scenes
Cameras can struggle with bright skies and dark foregrounds. A light meter allows you to measure key areas and expose them accordingly, preserving highlight and shadow detail.
Common Light Metering Mistakes
Relying Only on Reflected Readings
If you only use reflected metering, your exposure may be influenced by the subject’s brightness. Dark subjects can lead to overexposure, while bright subjects can cause underexposure. Incident metering is often more reliable.
Ignoring Light Direction
Light meters measure intensity but not direction. If you’re metering incident light, ensure the meter dome is facing the correct way—usually towards the camera or the main light source.
Forgetting to Adjust for Creative Intent
A light meter provides technical accuracy, but exposure is also about artistic intent. Adjust slightly to achieve the mood you want.
Do You Need a Light Meter in the Digital Age?
Many photographers assume that light meters are obsolete, given the real-time feedback on digital cameras.
However, professional photographers still use them for precise control, especially in portrait and studio settings. A light meter ensures consistency across multiple shots, which is critical for commercial work.
Even if you shoot digitally, knowing how to meter exposure manually will improve your understanding of light and exposure. Relying solely on camera automation can limit your ability to control the final image.
How to Use a DSLR Camera’s Built-In Light Meter
Modern digital DSLR cameras come equipped with a built-in light meter, which measures the brightness of a scene and helps determine the correct exposure settings.
While handheld light meters offer greater accuracy, your camera’s metering system is a powerful tool when used correctly.
Understanding the Built-In Light Meter
Your DSLR’s light meter works by reading the reflected light from a scene. The information is then displayed as an exposure scale in the viewfinder or on the LCD screen.
The meter evaluates the light and suggests adjustments to achieve what the camera considers a balanced exposure.
The exposure scale typically looks like this:
-3 -2 -1 0 +1 +2 +3
This scale represents stops of light.
- The middle mark (0) is what the camera considers the correct exposure.
- If the indicator moves to the left (negative side), the image will be underexposed (too dark).
- If it moves to the right (positive side), the image will be overexposed (too bright).
How to Read and Use the Exposure Scale
Step 1: Take the Camera out of AUTO Mode
To take full control of exposure metering, switch to Manual (M), Aperture Priority (Av/A), or Shutter Priority (Tv/S) mode. In Auto mode, the camera adjusts everything for you, limiting your control over exposure.
Step 2: Half-Press the Shutter to Activate the Meter
Point your camera at the subject and half-press the shutter button. This activates the built-in light meter, which will evaluate the lighting and display the exposure scale inside the viewfinder or on the LCD screen.
Step 3: Adjust Your Exposure Settings
The meter will indicate whether the image is too dark, too bright, or properly exposed. You can adjust one or more of the following settings to move the indicator toward the middle (0):
Aperture (f-stop): A wider aperture (lower f-number) lets in more light, moving the meter toward the positive side. A smaller aperture (higher f-number) reduces light, moving the meter to the negative side.
Shutter Speed: A slower shutter speed allows more light, while a faster shutter speed darkens the image.
ISO: Increasing the ISO makes the sensor more sensitive to light, brightening the exposure. Lowering the ISO reduces brightness but maintains better image quality.
Step 4: Re-Evaluate the Meter and Take the Shot
After adjusting the settings, check the meter again. If the indicator is close to the middle, your exposure should be well-balanced. If it’s still too far to the left or right, make further adjustments.
Different Metering Modes in DSLR Cameras
DSLR cameras offer different metering modes to control how the built-in meter evaluates light. These modes are crucial for achieving the best exposure in different situations.
Evaluative (Matrix) Metering
- Measures light from across the entire frame.
- Best for general photography, including landscapes and portraits.
Centre-Weighted Metering
- Prioritises the central portion of the frame while still considering surrounding areas.
- Useful for portraits where the subject is in the middle.
Spot Metering
- Measures light from a very small area (usually 2–5% of the frame).
- Ideal for high-contrast situations, like a backlit subject or a bright face against a dark background.
Practical Tips for Using a DSLR Light Meter
Avoid Extreme Highlights or Shadows – If shooting a high-contrast scene, spot meter on the mid-tones (not the brightest highlights or darkest shadows).
Use Exposure Compensation (+/- EV) – In Aperture or Shutter Priority mode, adjust the exposure compensation to brighten or darken the image without switching to full manual mode.
Check the Histogram – The light meter is a guide, but checking the histogram can confirm that you haven’t lost highlight or shadow details.
Final Thoughts
A light meter is a valuable tool for photographers who want greater control over their exposure metering. While modern cameras have advanced metering systems, they aren’t infallible.
If you’ve never used a handheld light meter before, give it a try. It may seem like an extra step at first, but once you see the benefits, you’ll wonder how you managed without one.
Your DSLR’s built-in light meter is an essential tool for how to meter exposure effectively.
By understanding how to read the exposure scale and adjust settings accordingly, you can achieve consistently well-exposed images in any lighting condition.
Mastering your camera’s metering modes will help you make better creative decisions, giving you greater control over your photography.
