Why you need an incident light meter for accurate exposure

We all know that light is the first consideration in photography. Everything else comes after that. Well, if light is so important, why do so many photographers take chances with their exposure settings? Read on to find out what an incident light meter is and why you need one.

Fixing a photograph on the computer afterwards will never be as good as getting the exposure right in camera. Aside from that, it’s a huge waste of time. I’d rather be photographing than fiddling with exposure in Lightroom or Photoshop.

Incident light meters used to be considered absolutely essential to photography. Every photographer used an incident light meter, but they were just called light meters, because there was the only type of light meter.

So what happened? Why are photographers not using incident light meters as much anymore?

What’s an incident light meter?

Incident light meters are hand held light meters. Like the light meter in your camera, it measures light so that you can adjust your camera settings and lighting to ensure accurate exposures. But how it measures the light is the key difference. More on that in a moment.

An incident light meter measures both natural light and flash.

Sekonic L-358 light meter for ambient light

A light meter set to measure ambient light. The F refers to the f-stop and the T is the shutter speed. I set the ISO to 200 (see top right) and the aperture to f4. I then measured the light and was given a shutter speed of 1/80.

Sekonic L-358 incident light meter

The light meter is set to measure flash. The ISO is set to 200 and the shutter speed is set to 200. When the flash triggers the light meter will measure the light and give me a reading of the f-stop, which is currently set to 0.

But my camera has a light meter

The obvious question then is what’s the point of another light meter if my camera already has one? Well, this one is different from the light meter in your camera and much more accurate.

Your camera’s light meter is great, but it’s not always correct and it can’t measure flash output. So you can’t use it for measuring off camera flash lighting.

Why you need a light meter for flash and ambient light readings

Lit with flash and backlit by the evening sun, both measured with an incident light meter.

The problem started with our all singing, all dancing digital cameras with inbuilt light meters and histograms. They’re incredible machines and most of us don’t use even 50% of the technology. It’s become a bad habit to…

  • Take a picture
  • Look at the LCD screen
  • If it looks good, fine
  • If it doesn’t look good
  • Adjust a thing or two and take another shot
  • And another
  • And another
  • If it’s still not right, fix it in Photoshop or Lightroom

You end up with a bunch of bad photos of the same thing before you get to what looks like a good photo. And that’s according to the screen on the back of your camera. Which you can’t see properly outdoors anyway.

After all that effort, you load your photos to your computer, and they don’t look as good as you thought. So disappointing! This is why you need an incident light meter.

How does an incident light meter differ from a camera’s light meter?

An incident light meter measures the light falling onto your subject. It can measure flash light and ambient light (whether it’s natural, tungsten, halogen etc etc).

A incident light meter will give you an accurate reading regardless of what the light falls on.

The light meter in your camera is a reflective light meter. It measures the light bouncing off your subject. It can only measure ambient light, not flash.

Your camera’s reflective light meter gets confused by really bright or really dark scenes and subjects. Examples are snow or a white sandy beach, or photographing a black cat on a black couch.

I know how to read a histogram, so I’m fine

If you know how to read your camera’s histogram, you’re one step ahead of many, which is great. You can keep shooting and adjusting until your histogram looks good.

Do you know the weaknesses of the histogram?

If you do, great! Chances are you get good exposures. But not always. Histograms aren’t exact so accuracy isn’t guaranteed.

How many photos did you take before you got to that good exposure? This is another good reason why you need a light meter.

Using a light meter to measure flash light

Imagine a guaranteed accurate exposure solution

What if there was a way that you could meter the exposure, dial in your settings and know that the image will be correctly exposed? No wasting time shooting the same thing over and over to get to a good exposure. That would seem like a good idea, right?

You could get the shot you wanted and move on quickly before…

  • The scene changes
  • Or your model/partner/friend/kids/dog, or worst of all, client gets bored and their expression becomes stale
  • Or the kids/dog stop cooperating and run off

Well, there’s a solution. A really good one!

Set your exposure quickly

With the advent of digital photography many photographers felt they didn’t need a hand held light meter, also called an incident light meter.

Things are changing. Photographers are going back to using an incident light meter.

Photographers are starting to realise that their camera’s inbuilt light meter has its failings. So they’re looking for a reliable way to cut down on all the faffing before getting the actual shot.

More photographers are using off camera flash now and they’re getting bogged down taking ages to set up a shoot.

Maybe not so much when using just one light, but more than one light complicates things. If you use two or more lights, without setting your lighting ratios using an incident light meter, you waste so much time and leave so much to chance. What’s more, every time you change set you have to reset your lights.

Save time setting up your lighting by using an incident light meter and you’ll have more time photographing.

When a handheld light meter isn’t useful

The one time an incident light meter isn’t essential with strobe photography is when using colored gels on lights. In this instance you have to go by what the image looks like, rather than an accurate meter reading.

Why don’t more photographers use incident light meters?

I often wonder this. Why would you spend huge amounts on gear and then ignore the one thing that can make your life easier and your photography better?

It might be:

  • A cost thing. Maybe because with digital you can shoot and check and shoot and check, people don’t want to spend on an incident light meter. Buy a used light meter.
  • An overwhelm thing. Learning to use a light meter is adding another layer of tech. It’s another thing to learn. Incident light meters are so easy to use, even if they don’t look it!
  • A knowledge thing. If more professional studio photographers told new photographers to learn how to use an incident light meter, it would be a normal thing. Seriously, get an incident light meter.

In summary – why you need an incident light meter

  • Guaranteed accurate exposure
  • Set your exposure quickly
  • Save time adjusting photos on the computer afterwards

I would never be without an incident light meter

I’ve had my current incident light meter, a Sekonic L-358, for at least 15 years. It lives in my bag and I’d never consider heading out to a shoot without it, even though I use Profoto lights that can be set to TTL mode. Every time my lights come out, so does my light meter.

Although I don’t use it for every natural light shoot, I do still use it a lot. 

The L-358 Sekonic light meter has been superseded, but you can still pick them up second hand for half the price of newer models. It’s 100% reliable and accurate – even after I accidentally left it in the grass outside my studio over a rainy weekend! It’ll continue to work for many, many years, saving me time on set and sparing me the disappointment of badly exposed photos.

Give it a go and you’ll understand why you need an incident light meter. You’ll never look back.

Leave a comment

If you have any questions about why you need an incident light meter or how to use an incident light meter, let us know in the comments.

Also, I love good news, so if my light meter tips have helped you to understand why you need an incident light meter, share that too.

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