Whether it's built into a camera or is a hand-held device, a light-meter measures the intensity of light.

We simply enter in the ISO and the meter creates a formula for what the Shutter-Speed and Aperture settings should be.

Automatic cameras (like mobile devices) do not allow us direct access to the light-meter. We never see their meter working, but it is.

This graphic represents the typical light-meter display in an SLR camera, while some older film cameras use a sweeping needle instead of lighted bars.

This meter uses individual bars, each one illuminated based on the amount of light being detected in that particular region.

If the only bar illuminated is in the middle ("0"), then according to the meter, we have a balanced exposure.

If the lighted bars push more into the positive (+) end of the meter, I am over-exposed. Meaning the exposure has too much light.

Lighted bars in the negative territory (-), indicate I am under-exposed. I have too little light.

Whether automatic or fully-manual, everything depends on getting an accurate light-meter reading of our subject. Failure to do so means our exposure equation (ISO+Shutter-Speed+Aperture) will be wrong right from the very beginning and our photographs don't come out.

So it's important to understand just how cameras SEE and RECORD the world, sometimes the light-meter is wrong and we need to know what to do.

There are two kinds light-meters: Reflected and Incident

Reflected light-meter is the most common one, and is built into cameras. It measures the light being reflected off our subjects, whether it's a hummingbird or a mountain.

This type of meter evaluates the world not in color, but in shades of gray (tones).

It searches for the halfway point between full-black and full-white (something called 18% gray) and sets the exposure based on that.

The downside to reflected metering is a very bright scene like the sun, snow, a sandy beach, a lamp or any large bright surface. The reflected meter is fooled by the brightness and will adjust the exposure downwards to compensate.

Our image is now under-exposed and the nice white snow we see has been replaced by a lighter shade of gray.

Likewise, if we're photographing a large black surface, such as a monument, this also will not be represented accurately, either. The exposure will be shifted upwards to a dark shade of gray, over-exposing our image.

An incident light-meter is a hand-held device.

This kind of meter measures the amount of light falling on our subject. We can be photographing something right in front of us or a mountain miles away.

As long as we are all in the same light, the exposure will be accurate.

Incident meters are not fooled by reflecting light, either.

Snow is rendered as being white and not gray. The same with a black monument.

The downside to an incident meter happens when shooting outdoors. If our light is constantly changing, it may require us to monitor the changing light conditions. Many incident meters have the ability to also read reflected light, increasing their versatility

Plug-in accessories are available to turn smartphones into incident meters..

In many cases getting a good photograph requires that we take control and set the properties ourselves. In this case, I was at the Keene Pumpkin Festival and took 2 photographs. With one, I just pointed the camera and took the photograph in full-automatic mode where the bright street lights were part of the metering equation. Notice how dark it is.

In the second photograph, I went full-manual and pointed the camera down, metering solely on the pumpkins. I adjusted ISO, Shutter-Speed and Aperture to what my reflected light-meter indicated was a good balanced exposure and took the photograph.

Clearly the better photograph of the two.

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