Photography 101.8 - The Light Meter

Photography 101.8 – The Light Meter

Photo 101.8 Light Meter

Photo: Rainer Ebert - CC license

The following post is from Australian photographer Neil Creek who will soon be teaching a class in portrait photography in Melbourne Australia, and is developing his blog as a resource for the passionate photographer.

Welcome to the seventh lesson in Photography 101 – A Basic Course on the Camera. In this series, we cover all the basics of camera design and use. We talk about the ‘exposure triangle’: shutter speed, aperture and ISO. We talk about focus, depth of field and sharpness, as well as how lenses work, what focal lengths mean and how they put light on the sensor. We also look at the camera itself, how it works, what all the options mean and how they affect your photos.

This week’s lesson is The Light Meter.

Here’s What We’ve Covered Previously in this Series:

Lesson 1: Light and the Pinhole Camera
Lesson 2: Lenses and Focus
Lesson 3: Lenses, Light and Magnification
Lesson 4: Exposure and Stops
Lesson 5: Aperture
Lesson 6: Shutter
Lesson 7: ISO

In previous lessons we have talked about the basic theory of how a camera works, including some basic optics, and introduced the idea of exposure and how we control it with the exposure triangle. Now that we have covered each of the points of the exposure triangle, it’s time to bring them all together with the tool at the core, the light meter.

What is the Light Meter?

Sunset at Chelsea Beach

A challenging scene to meter

For as long as people have been taking photos, there has been a need to determine how bright a scene is. Any method of recording light can only work in a relatively narrow band without over or under exposing the image. To find the correct exposure that will record the image without over or under exposing it too much, photographers need to know how bright the scene is. An extremely talented photographer may be able to guess a near-enough exposure, but a light meter is a far more accurate and convenient way to do it.

Light meters in cameras react to how intense the light is as seen from the camera. SLRs measure the light (called metering) through the lens – TTL. They collect light that has actually passed through the camera’s lens and measure its intensity. There are problems when the scene has parts that are much brighter or darker than others, for example shadows on a sunny day. This can trick the light meter into measuring the intensity of the light incorrectly, depending on which part of the scene was illuminating the sensor.

Modern SLR cameras use multi-point light meters, meaning that several light meters are actually scattered around the projected scene, each measuring the light intensity at that point. Very sophistocated cameras may have dozens of metering points. How much the measured intensity of the light at each point influences the final meter reading depends on the metering mode selected by the photographer.

For a more detailed look at metering modes, you can read: Introduction to metering modes.

How to Use the Light Meter

Mode Dial

As we now know, the correct exposure is created by juggling the three points of the exposure triangle: aperture, shutter and ISO. The light meter is the tool that puts us in the right neighbourhood for how these should be set. If you are shooting on full auto, then when you meter the scene – usually done at the same time as focusing, by half pressing the shutter – the light meter gives its best guess for each of these variables.

If you want to take creative control of the photo, you can manually set each of the three variables yourself. Typically ISO is left at the default, or previous setting, and you take control by choosing aperture priority or shutter priority. On most DSLRs that’s done by turning the exposure mode dial. If you set the dial to Av – aperture priority, the photographer chooses what the aperture will be, and the light meter adjusts the shutter speed to mantain the correct exposure. The reverse is true for Tv – shutter priority.

When using these modes, it’s useful to refer to the exposure meter display on the camera. The exposure meter (display) shows the result of the measurement taken by the light meter (sensor). It will typically look something like this:

Exposure meter display on LCD

Exposure meter display on LCD

Exposure meter display in viewfinder

Exposure meter display in viewfinder

Each number represents a stop change in the light, as indicated, with the central mark being the “correct” exposure, as determined by the light meter. Each pip between the numbers represents one third of a stop. The arrow underneath indicates how close the current settings are to the correct exposure. Usually in priority modes, the arrow will stay in the middle as the light meter will be able to set the exposure correctly. However, if for example you set your aperture to 1/400sec in Tv (shutter priority mode) and the light meter indicated that you needed an aperture of f4, but your lens was only capable of f5.8, then the exposure meter will display one stop of underexposure. You will need to compensate for this by setting a longer shutter time, or increasing the ISO.

The juggling act becomes more complicated, and the light meter’s assistance more valuable, when you go to full manual control of the exposure. Here the exposure meter simply displays whether the current settings will under or over expose the image, according to the light meter. The photographer can freely change any of the values on the exposure triangle, and see the change to the predicted versus recommended exposure.

Exposure compensation

Even though the light meter in your camera is pretty sophistocated, sometimes it can get it wrong, especially with harsh contrasts, or highly reflective surfaces. Changing metering modes may help this, but a more controlled approach is to use exposure compensation. Imagine you are photographing a person against a large bright sky. The light meter thinks the sky is the most important part, and exposes correctly for that, leaving the person a dark silhouette. By using exposure compensation, you can tell the camera to take the metered exposure and make it brighter by a chosen amount. This will then allow the photographer to correctly expose the person. I’ll look at exposure compensation in more detail in a future post.


To show you how the different exposure modes might work in real world situations, here are some scenarios. The settings given below are what they happened to be for the examples shown. Settings for your own photo will be different.

Scanario 1 – Sports

  • High speed is needed to freeze action
  • Use Shutter Priority
  • Set shutter speed to 1/800sec
  • The light meter sets the aperture to f10
  • If under exposed, change ISO to compensate – ISO400

Kite Surfer

Scanario 2 – Portrait

  • An artistic narrow depth of field is desired
  • Use Aperture Priority
  • Set aperture to f5.6
  • The light meter sets the shutter to 1/160sec
  • If under exposed, change ISO to compensate – ISO100

Siera on a Swing

Scenario 3 – Night scenery

  • Ambient light is too low to accurately meter
  • Use full Manual
  • Set aperture to suit scene, erring to wider – f11
  • Set a long shutter speed to light meter’s best guess – 20sec
  • Set ISO to lowest possible for correct exposure – ISO100
  • Take a test shot and adjust settings if the light meter got it wrong

2009 New Years Fireworks

Scenario 4 – Off-camera manual flash

  • On auto, meter the scene and note settings
  • Set camera to one or two stops under exposed
  • Set up flashes and tweak power to expose correctly
  • Tweak the flashes exposure by adjusting aperture
  • Tweak the ambient light by adjusting shutter speed
  • Settings for example shot: 1/160sec f8 ISO125, click image for flash details.

Siera and Annie


  • Put the camera in auto mode and half press the shutter. While looking through the viewfinder, pan around a scene and see how the automatically selected camera settings – f ratio and shutter speed – change. This preview will disappear after a few seconds, so half press the shutter again for another look.
  • Set the camera in shutter priority mode and choose a shutter speed for effect, eg: short for sports, long for motion blur. Shoot different scenes and note how the camera adjusts the aperture to balance the exposure.
  • Do the same as above for aperture – wide for shallow depth of field, narrow for focus detail at all distances.
  • Get adventurous and put the camera on full manual. Adjust the camera settings yourself, and watch the arrow below the exposure meter. Tweak the settings to get the arrow in the middle of the meter – half press the shutter while looking at your scene to take a meter reading.
  • Try to apply what you have learned to make creative photos that take advantage of the different exposure modes.


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Neil Creek is a professional photographer from Melbourne, Australia. He has been shooting with a DSLR since 2004, and blogging about his experiences since 2006. Neil has authored five ebooks and a video training course, all designed to help others improve their photography. View Neil's folio at his home page. Learn about his publications here.

Some Older Comments

  • Gary August 2, 2013 06:59 am

    thanks for sharing this great tutorial. had a go and my results have been 100% better. been trying to get my head around metering so thanks!!

  • sandro October 4, 2012 07:16 pm

    Hi Neil,

    I have absorbed your lessons like a sponge.. just great learning here. Is there any way I can link to the next lessons i can't seem to find a link?

    thanks mate

  • Biji Joseph March 30, 2012 11:39 pm


    I came across these articles of yours while browsing through the net for articles on understanding the science / logic behind digital photography. Your notes and lessons have been a great learning - quite different from the other sites that concentrate on the "how" rather than the "why"

    I was able to get through till Lesson 7 on the Light meter. Beyond that I was not able to see any further links. Could you please guide me on where to access the next lessons.

  • Dimple January 12, 2010 05:57 am

    Thank you so much. That worked.

  • AlexO January 10, 2010 09:45 am

    I don't want to talk on behalf of this website but I will try and give you a quick answer.
    From what you(dimple) described, it is very clear that somebody or you(without knowing) dialed exposure compensation in your camera in the value of +2. In the AEB, camera adds/removes the same amount of exposure compensation to/from the current value which is +2 in your case. So if you want to shoot with AEB with the +/-2, your camera will display 0 and +4 because adding +/-2 to currently +2 will result in -2+2=0 on the low side and +2+2=4 on the high side. Your camera is doing exactly what it is supposed to do so there is nothing wrong with your camera.
    And it is very easy to set your exposure compensation back to 0. Just refer to your instruction manual. I do not know what camera you are using but I can tell that it is a Canon from the Tv, Av shooting names you mentioned. And since you have AEB in your camera, I also assume that it is a digital SLR camera.
    Look for a button with "+/-" mark on it. Press on that and then use either left and right arrows or a dial(you will probably have a dial on your camera) to set that +2 back to zero. If you have a Rebel series camera, you will need to press and hold that "+/-" button while rotating the dial.
    One last thing, I would suggest you post these type of questions on a forum to get much quicker help.

  • Dimple January 9, 2010 07:47 am

    when I am in Av or Tv mode, my exposure meter always reads +2. I think it should be showing 0 (balanced exposure) but I cannot get it to 0.

    Second, on AEB, the scale runs from 0 - +4 instead of -2 to +2.

    I think there is something wrong here but I don't know how to balance my exposure to 0 and change the scale in AEB but I do think they may be related to the same issue. Can anyone help me solve this?


  • Mel January 8, 2010 12:57 pm

    ISO, aperture and shutter speed, everyone has their own style of photography, I dig long shutter speeds even with my subject in motion. there is no right or wrong, each they're own!

  • AlexO December 8, 2009 03:49 pm

    Also in the paragraph right under where the exposure meter display on LCD, it says:

    "However, if for example you set your aperture to 1/400sec in Tv (shutter priority mode) and the light meter indicated that you needed an aperture of f4,..."

    Where it says "aperture" should have been "Shutter Speed". This is a simple typo and I am sure most of you got it already but some people may get confused. So it would be nice for Neil to fix it...

  • Nikki September 25, 2009 04:48 am

    I am currently taking a course on digital photography and we are learning about light metering. I completely understand the "WHYS", but I feel like everywhere I turn, I cannot get the "HOW". It's hard for me to relate the light metering to real life situations. The grey scale makes sense. I need someone to tell me step by step what to do. I think I might have the light meter confused with the exposure setting. During my class, my instructor told us to put our camera's in Auto and set the exposure to 0.0 (I have a Nikon D60). Did that. OK, then in Manual (which is the only setting I ever use) take a picture of a grey card. I am completely lost at that point. It just doesn't want to sink in. I have a family photo session this weekend and I'm worried I'm going to be concentrating on getting that right so much, that I'm going to do a terrible job. There will be 3 of them I'm photographing and they will be wearing dark blue and purple shirts. What am I supposed to do? I would so much appreciate someone's explanation!!

  • Charlie Stott August 27, 2009 06:54 am

    Thanks for this course. I've been taking photos for 25 years or more, but only just gone digital, and thought "why not go back to basics at the same?". I am very glad I did. I really enjoyed the technical discussion of how lens and camera 'read' light. Is this the last in the series? I can't find links to the next lesson. Is there more coming, it seems to end so abruptly.

  • Chris August 16, 2009 01:36 am

    I have a Nikon D40 and use minus 7 exposure compensation the same is also on the D80 and it usually comes out correct within the histogram and does not clip the highlights.

  • Martin Barabe July 19, 2009 12:35 am

    Thank you Adam for the info.

  • Adam July 18, 2009 02:04 pm


    As Dom mentions above, the camera's light meter will try to go for "18% grey" (I understand this to mean halfway between black and white by luminance). This is very helpful, and is a sensible sort of thing to do, but doesn't always lead to the best photograph.
    It isn't a fault with your camera, or with your photography - if you know you like shots that are one stop down from the camera's light meter, use the exposure compensation setting and you'll be set. Don't be afraid to try photos that are further away though, sometimes you can get much more evocative images this way.

  • Martin Barabe July 18, 2009 12:16 pm


    long exposure speed will also result in noise, the correct way is to balance out everything to your satisfaction criteria.

    I Only recently realized what those bars with numbers were on my camera, (i am very new to photographie). Since i found out that this was metering, i started playing around with it and found it to be very effective way to get my shots right the first time since i shoot in manual mode and constantly play with all my settings.
    one thing i found is i always have to get my exposure on the camera metering one stop lower than recomendation to get the exposure to my liking, Why is it this way? I have a Canon XS camera.

  • Nitharia Photography July 17, 2009 02:57 pm

    Play with shutter speed and aperture....iso will result in noise

  • Adam July 17, 2009 09:08 am

    I really like that example you give, Pat - Using the ISO to effectively change the aperture when in Shutter Priority mode. I've always had it in my head that if you're in Shutter Priority mode it is because you're not concerned with the aperture, but this has opened my eyes!

    I think a bunch of discussion on the scenarios is ok - that's what comments are for...

  • Dom July 17, 2009 07:19 am

    I agree with gabor's comment regarding middle gray. Too many photographers fail to realize that the meter drives everything to 18% gray. Unless you can take that into account using the zone system or you use a gray card, letting the camera's meter do the thinking is not the way to go. Once a photographer masters the ability to manipulate 18% gray, he won't have to chimp the camera screen to see if he got the exposure correct.

    I agree with Alex's comment, being a fellow strobist, on how to set up off camera flash. The one part I don't agree with is letting the camera figure out the correct exposure.

    I don't agree with Eric's subsequent comment regarding keeping the subjects still. If the shutter speed is slow, but reasonable, say faster than 1 sec, the flash will freeze them appropriately even if they twitch. That is due to the speed of the flash which is way faster than the shutter speed (~1/8000 of a sec or faster).

  • Pat Bloomfield July 17, 2009 05:33 am

    I think this article is a nice introduction and perhaps we're bringing too much into Neil's offered scenarios.

    He is absolutely correct that you can control your exposure to your advantage by changing the ISO. However as rightly pointed out if the camera is in auto mode it will simply shoot the equivalent exposure. The only way to correct this in aperture or shutter priority is to change the exposure compensation. But to show an example of how changing the ISO can be used to get the desired picture results:

    Picture this real example from when I used to photograph motor sports; you want a shutter speed of 1/500s and you also want to shoot wide open to blur the background and get separation of your subject. Assuming you have to correct exposure compensation to get the right exposure, you set your camera to 1/500s shutter shutter priority. You then reduce your ISO enough so that you're shooting around f/2.8 - f/4. If it's really bright sun light you won't be able to get that wide but you go as wide as possible. As the light levels drop you will eventually find that the camera starts to underexpose because the shutter speed is fixed and the lens is as wide open as it will go. You can now correct the situation by increasing the ISO a stop or two so the camera is able to produce correct exposures within the set parameters. This is the effect that I believe Neil was referring to. It is all about taking control of your camera to produce the effects that you desire.

    What Neil does not mention here is that this is a reflected meter reading and not incidence, so the meter will be fooled when measuring dark or light scenes. This is because it will always average the scene to 18% grey. Probably too advanced for this article but if you want to do further reading check out zone metering for digital photography.

    Another point of note is that your camera meter probably under exposes between 1/2 to 1 stop. Once you have tested your camera you can compensate for this. For example my Canon 1Ds and 10D under expose by 2/3 stop while my newer 5D only underexposes by 1/3 stop. See how accurate your camera exposure is.

    Pat Bloomfield
    Suffolk Wedding Photography

  • Rick July 16, 2009 04:10 am

    Adam. You are correct wrt Scenario 3 but I think the author meant you should set the lens to err on a wider depth of field by his comments. Now to get that wider DOF, you have to use a smaller or narrower aperture as you noted.

  • Chris Velez July 16, 2009 02:29 am

    This is something that I have found to be a great tool as far as exposure is concerned.

  • Eric Mesa July 15, 2009 11:44 pm

    Alex - most important thing, though, is if your ambient drops the shutter speed too low, your subjects need to know to stay still and not move when the flash goes off. Or maybe use second curtain flash.

  • Alex Pounds July 15, 2009 06:49 pm

    Personally, when working with off-camera flash I do things the other way – get the ambient right first, then add flash. Often this will involve letting the camera pick the 'correct' exposure, then using exposure compensation to drop things down a notch. You can then add flash to bring your subject up to a correct expsoure, and adjust your flash using either aperture or flash power. I picked this technique up from Strobist.

  • Adam July 15, 2009 06:31 pm

    Bracketing (useful, as Miguel pointed out) is where you take the photo and then adjust one of the points of the exposure triangle up one stop, take another photo, adjust down one stop, and take a third photo.
    This can be done with more or less photos, smaller or larger stop adjustments and with different parts of the triangle, but the end result is the same: If you only realise later that you stuffed it up, you've got back up.
    Some cameras can do bracketing automatically. It can also later be used for HDR.

    In addition (mostly for those 101 types who may get confused by such errors) it would be nice if the author could authoritatively comment on the inaccuracies noted above. My 2c is to ask how the ISO changes mentioned can mean anything - it wasn't stated what the ISO was changed from.
    I'd concur that changing the ISO wouldn't work, unless you were at the bounds of what the camera's auto setting would reach to.

    I'd also like to question a detail of Scenario 3:
    "Set aperture to suit scene, erring to wider - f11"
    f11 is a narrow, not a wide aperture. A narrow aperture is desirable here as it gives greater depth of field so the buildings are more likely to be in focus.
    Again - I point this out in the hopes of preventing people new to photography getting confused. I know that it confused me no end trying to figure out the wide - narrow / small number - big number set up.

  • MeiTeng July 15, 2009 12:37 pm

    I echo Dimitri's question to Portrait 2.

  • Miguel July 15, 2009 08:12 am

    This is a great resource for any photographer. Exposure compensation is very important and learning the importance of bracketing. Great post!

  • Gábor July 15, 2009 07:03 am

    What I don't like about light meters that they want everything to be middle gray. (of course, that's the way they should work..) I strongly recommend using the mentioned exposure compensation. I found Ansel Adams' zone method, which involves spot metering AND your consideration of exposure, to be quite effective, at least on still subjects / landscapes, etc..

  • fromBrandon July 15, 2009 05:42 am

    I have really been working on my metering abilities lately, but what I really struggle with is knowing what to meter off of. I hate having to rely on looking at my LCD to make sure things look right before I can move on. I want to be more efficient with my metering, but it is a challenge.

  • Rick July 15, 2009 03:52 am

    I think Scenario 1 and 2 are in error. If you have an underexposed picture, adjusting the ISO will not help in either case. In 1: Tv, 1/800, f10 and under exposed. Increasing ISO from 200 to 400 for example would result in Tv, 1/800, f14 and still under exposed. In 2: Av, 1/160, f5.6. Increasing ISO from 100 to 200 would result in Av, 1/320, f5.6 and still under exposed. In both cases if they are under exposed due to metering errors, the only way to fix this is with manual exposure or with exposure compensation. There is a case in Tv that increasing the ISO could help. This would be the case when the camera tries to open up the lens wider than the maximum aperture of the lens. In this case increasing the ISO would help. However that was not the example since you are a f10 and most lenses go at least to f5.6.

  • Dimitri July 15, 2009 03:42 am

    In Scenario 2, the Portrait, you recommended changing the ISO to 100 if under exposed. Is that correct? Wouldn't you change the ISO to a higher number if the picture is under exposed and a lower ISO if the picture is over exposed?