Basic Understanding Of Light & Need For Light Metering.

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Photography is nothing but recording light (in an aesthetic manner). Hence, it is imperative that we, as photographers, are required to measure and quantify the amount of light available so that we can use the corresponding settings on our camera to get a well-exposed and an appropriate image.

Buddhist Monns

Light meter is just that device that helps us measure the available light in our scene. Earlier, when people used film cameras and SLRs, most cameras did not have a built-in light meter. The photographers generally carried a separate incident light meter with them. Back then, photographers couldn’t even see if the shot they just took was well exposed as they were shooting in film. Hence, they heavily relied on the external light meter for exposure. With the advent of digital photography, we are blessed in more ways than I can count .

light meter

Types of light metering:

Light metering can be classified into two major categories:

  • Incident Light Metering
  • Reflected Light Metering

Don’t worry so much, I will explain it ALL. Just keep reading.

Fundamentals of light:

When you are photographing any subject, in essence you have two types of light:

  • Incident Light (Light that falls on the subject from a source of light)
  • Reflected Light (Light that is reflected from that subject towards the camera)
Incident Reflected Light

Understanding this fundamental difference between incident and reflected light is important because of the very fundamental nature of light. As you already know, visible light is only a very small portion of the electromagnetic spectrum. Colors, as we experience in our day-to-day life, DO NOT exist physically; they are a manifestation of our brain. Colors are an illusion.

electromagnetic spectrum

Let me break this down for you.

White light is the combination of different wavelengths of light. Every color has a different wavelength. A very common example of white light is sunlight. When white light falls on any subject which is say blue in color, the reason that object looks blue to us is because that object absorbs all the other wavelengths of light and reflects back ONLY blue light. White-colored objects reflect all colors of light, while black-colored objects reflect NO light at all.

Application in photography:

The way we measure incident light in photography is by holding a light meter in front of the subject and taking a reading. It is the measure of the amount of light falling on the subject.

Incident Light Meter
Photo Credit :

Reflective light metering is a little different. We generally use reflective light metering while using our camera’s TTL (Through The Lens) metering. That literally means the amount of light that gets reflected off the subject and comes in through the lens. We measure just that incoming light, NOT the actual amount of light falling on the subject.

Light meter
Photo Credit:

Our camera’s plight:

Our cameras are in a constant quest to understand the type of subject we are shooting and more importantly exposing EVERYTHING in the scene properly. This quest of exposing EVERYTHING properly sometimes leads to many problems.


For the camera, the definition of a proper exposure is 18% grey. So when you point your camera at a particular subject, the camera analyses all the light that is coming in (TTL metering) and then adjusts its settings so that it can achieve that 18% grey exposure. This system of monitoring, analyzing and settings selection works pretty well until there are some challenging scenes to shoot; like scenes which do not have uniform lighting throughout the frame.

Dynamic Range

Example: Shooting a person indoors or in a shade while the background is very bright as compared to the person.

The problem that arises here is that the different intensities of light present in the same scene is too much for the camera to handle. What the camera tries to do again is shoot for 18% grey and hence depending on the amount of sky or the person you include in the frame, you are going to either overexpose the sky or underexpose the person who would then most likely turn out very dark or just a silhouette.

Light Meter Sun

The camera then records very little or no data from the parts of the frame that are either absolutely black or absolutely white. The results are hence pretty terrible too, the sky when overexposed looks like a white featureless backdrop with no texture or details. On the other hand, if the sky is properly exposed but the person is not, he would look dark and probably only the outline of that person would be visible. Not a great portrait shot. Moreover extremely underexposed or overexposed areas cannot even be revived in post production. Not everything can be fixed on the computer darling!

An Easy Experiment:

It is very easy to demonstrate how our camera’s in-built TTL (Through The Lens) light metering works through an experiment. You can do it right NOW with me. Follow the steps below and you will understand the basic principle of your camera light meter in NO time:

  • Turn your mode dial and select the manual mode on your camera.
  • You are trying to be a good photographer and not a wannabe photographer so stop using the Live View for everything and look through the viewfinder. You should be able to find a scale at the bottom with ‘0’ (zero) in the middle. This is your light meter scale.
  •  Now while looking through the viewfinder, point your camera to a bright object like a light bulb. The scale should begin to slide towards the positive side.
  • Now without changing any settings on the camera, point it towards a dark part of the room where there is not much light. You will see that the scale now slides towards the negative side.

Note: The camera may turn off the light meter after a time period automatically. If you do not see the light meter scale, press the shutter button halfway and the meter should come back right on.


So what we are essentially doing in this experiment is analyzing the amount of available light in the frame. When you point your camera at a bright object like a glowing bulb, the camera looks at it and thinks “…so bright and so much light! I do not need so much light for a photograph. I must do something so that I can reduce the amount of light that I record, in order for me to properly expose the bulb”.

light bulb

It is because you are in manual mode the camera cannot do anything to change a setting required for a proper exposure. It is gives you a light meter reading on the positive side which means if you take a picture with this exact setting you are going to OVEREXPOSE the picture. On the flip side if the scale shows any value in the negative, like when you point the camera towards a dimly lit part of your room; the camera is telling you that the picture will be UNDEREXPOSED it you take it with this particular setting. Zero ‘0’ on the scale represents proper exposure.

Importance of learning:

I cannot emphasize enough, how important it is for ANY photographer to understand his light meter. Light is what ALL we as photographers play around with and it is not that hard to understand it. A little patience and practice will work wonders for you, I promise.

So play around with your camera light meter and try to understand it better. This is your first practice round. When you have understood the light meter BASICS well enough read up the next part:

Light Metering Modes | When To Use What & Why?

I will meet you in the next one.


Also published on Medium.