Picture a strong shaft of sunlight beaming in through your bedroom window. You can probably see little specks of dust floating through it, but, aside from that, you should notice one very important thing: you can't see the light itself. Between the sun and the time and place where it hits your hand, light is actually sort of invisible.

Light doesn't fill up a room like smoke. Instead, light assumes a position. When shooting professionally, it pays to know what's going on in a quantifiable way that the camera will be able to relate to. Light meters act as our "eyes" on the field. They show us what we can't see on our own.

What Is a Light Meter?

Sekonic Light Meter

To put it plainly, a light meter reads the strength of light. All digital cameras come outfitted with their own internal spot meters, which you'll recognize as the little ruled scale at the bottom of your viewfinder.

Spot metering is one way to read the light. Incidental light reading, or ambient light reading, is used to "catch" the light in a given spot and ascertain how it's falling on the subject as they stand on their mark. With this reading, you'll be able to make any necessary adjustments in order to find the value that you need for the shot.

If your camera already has a spot meter, you may be wondering why you need to bother with an external light meter. The difference is simple: incidental readings measure light in transit between the source of the light and the subject. Spot readings measure the light that actually ends up making it to your camera.

The light meters we see here are all capable of taking incidental readings; cameras on their own are generally only able to take spot readings. Both are useful in their own ways, and your preference will depend on your own personal style of shooting.

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The Benefits of Using a Light Meter

Vintage Light Meter

For many of us, when it comes to our problems in life, the less we know, the better. In the world of photography, however, you may find the opposite to be true. There is a sense of empowerment that comes with knowing exactly what you've got on your plate.

The biggest advantage of using a bonafide incidental light meter is that your readings will not be influenced by the characteristics of your subject—incidental metering is concerned with cast light, not reflected light.

Let's say you have two models, one with dark skin, and one with fair skin. The spot meter in your camera will yield two different values, depending on whose skin you've asked the camera to take the spot sample from. But what if you just want to see how much light is falling on them both to begin with? This is where a light meter comes in.

The more you know about the light that you're working with, the more precisely you'll be able to adjust it to meet your needs. Taking many incidental readings as you work through each setup will show you exactly how much each tweak strengthens or weakens the source.

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While some of us have an understanding of things like the inverse square law at our command, a machine reading eliminates the guesswork entirely. We can identify a problem that we see and address it at the source, as opposed to hunting and pecking mindlessly for a solution.

One thing worth mentioning about light metering, in general, is that it does take time. This really is the only drawback to using a light meter, aside from the price tag. If accuracy is something that you value, the knowledge that each reading affords you will be well worth the wait.

If you shoot candids just for fun, there's no reason to make the upgrade. If you shoot photos professionally, however, a light meter is the ultimate failsafe. You'll never be in the dark again, so to speak.

Is a Light Meter Worth It?

Light meters are probably one of the coolest photography gadgets out there. That, and they look pretty awesome hanging around your neck like a huge gold medal. What can we say? We like the attention.

If this toy has been on your wishlist for a while, it might be time to make the investment. You don't necessarily need a Sekonic in order to make your work shine—in fact, if you can master the art of converting lumens to stops, you might be able to find yourself a great DIY light meter from Home Depot. But you didn't hear it from us.