understanding lighting ratio
A Simple 3-part explanation 

1.definition of lighting ratio

The lighting ratio in photography is simply a comparison of the amount of light that is supplied by the main light compared to the amount of secondary fill light that hits the shadow areas.

You use the main light to highlight the shape and dimension of your subject and you use the fill light to control the contrast. A stronger fill light will lighten the shadow areas and give you less contrast. 

Why does it matter? These ratios are used more in portrait photography and cinematography than any other type of photography.

The Relationship Between The
Main Light and Fill Light Areas

2. The IMPORTANCE of the relationship between shadow and highlights

This lighting relationship is important because it dramatically affects the look and feel of every single photograph you take. Let's check out the comparison of the different lighting ratios in the portraits of Mabel the mannequin below. On the left you have the lighting that had the least amount of fill light and has the most contrast.

Left to right, each photo has twice as much fill light to lighten the shadows.

3. how to measure and calculate lighting ratio

Polaris Light Meter

If you want to be able to accurately measure lighting ratios, you need a light meter. You can approximate it by adjusting the distances of your lights to the subject, or vary their brightnesses, but that can get tricky depending on their size and shape.

This Polaris light meter has served me well for over 35 years. I used it to write this article and it reminded me of the good old days when you had to depend on a light meter just to get the right exposure on every photo you took.

You really don't "need" one at all in today's world of digital photography. You can view your exposure on your camera's LCD screen and make a  judgement on the contrast and shadow-to-highlight ratio subjectively.

Writing this article also reminded me of how much fun it was to tinker around with lighting and a light meter. It's one of those geeky photography tools that you can enjoy using if you're a lighting nerd like me.

To use it for setting up light ratio, it's critical that you use it to measure each light source independently without the second light interfering with your meter reading.

Use a light meter to measure both the bright and darker spots on your subject.

Light meters give you your brightness readings in f/stops, which is the lens opening the meter is telling you to use. Here's the trick. Each f/stop represents a doubling (or halving) of the light. An f/stop of f/4.0 on your meter tells you that that area is receiving only half as much light as an area where the meter says f/5.6. Here's a simple chart that shows you the common sequence of f/stops. 

Lighting Ratio Chart: Each lens f/stop number lets in half or twice the amount of light

• In the example above you took a measurement from your key light of f/5.6. Then, you measured your fill light area and get a reading of f/4.0. This will lead you to a lighting contrast ratio of 2:1 because there is one f/stop between f/4.0 and f/5.6 and each stop doubles the amount of light.
• If the highlight area gave you a reading of f/8.0, then it's two f/stops (twice the light per f/stop) = four times as much light at f/8.0 than at f/4.0. So, f/4.0 and f/8.0 would be a 4:1 or 4x lighting ratio.

Here's the simple setup I used to make the initial photos shown in the beginning of this article. I used Novatron (discontinued manufacturer) lights and the standard incandescent bulbs as a continuous light source and not their flash capabilities.

portrait Lighting setup

This is how I photographed Mabel the mannequin in the example above. It was a simple lighting setup, done in my TV room with the window shade pulled down to provide a simple background for my always cooperative model.

Simple Lighting Setup

compare these two examples of lighting ratios

But wait, there's more! Here's another example. Rather than use the human face,  this illustration is a simple still life photo of my favorite vessel for craft beer along with a frosted mug. You can use your mouse cursor on and off the photo to see the difference in the ratio between the two photos.

Scroll over this with your mouse

The Set-up for this still life photo

This comparison shows a somewhat subtle, but still significant difference in the two photos. 

The photo, where did I did not use the reflector, actually has a small amount of fill light coming from the white painted cinder blocks in my basement, where these photos were taken. But the fill is not nearly as much as when I moved in the large reflector panel close to the subject.

Notice how the fill light also had a significant effect on how the background rendered. Both the softbox and the reflector panel are quite large in comparison with the mug and growler and this combination will give you very soft look with light scattering in all directions.

high contrast ratio

The sunset photo below shows a natural setting with no control over the contrast ratio. Although the sun was diffused from passing through the clouds the lighting ratio was likely in the hundreds. Essentially, in a situation like this, you are photographing the actual light source with a tremendous amount of light entering directly into your camera and striking the sensor.

Fortescue NJ Sunset

The fill light that was hitting the dock on my side was minimal compared to the brightness of the sun. Lesson learned: Sometimes experimenting with super contrasty lighting can give you some very interesting photos.

Bottom line, you will rarely ever have to use an exact lighting ratio in your photography, but it's very helpful for you to know what it is and plan or design your lighting based on the effect you want to achieve. If this article was helpful, please share it.

ABOUT BRUCE LOVELACE

Bruce is the publisher of this website. He is the author of the book "Improve Your Photography Instantly."  Read more on Bruce on his Bio Page. He's been known as The Traveling Photographer ever since 1994. Read more about this website.

View some of Bruce's photos on Instagram.   Visit the Facebook Page. Watch him on YouTube.  Bruce runs photo workshops for kids and adults, and provides one-on-one photography coaching.

Digital Photography Education Location on Google My Business

Shadow Photography at Home

Return To Photography Lighting

Another Guide On How to Use Ratios in Lighting

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examples of contrasty light ratios

Big Highlight to Shadow Light Ratio

At this angle, the main light (sometimes referred to as the "key" light) does a great job of showing the beauty and form of the female face.

Mysterious Effect With No Fill Light

The key light is so high above the subject's head and the absence of fill light make this photo very secretive. Do you think this gentleman is feeling content and at peace or is he in a state of anxiety or depression?

Lighting Ratio Creates Eerie Effect

The bare fluorescent bulb is the only source of light in this image so there really is no lighting ratio to calculate. My own opinion is that it would be more powerful photo if a different shirt had been chosen.

Low Lighting Ratio is about 2:1

examples of low lighting ratios

There are shadow areas with this lighting, but the ratio between the highlights and shadows is small. I posed this couple in the open shade of a building and there was a lot of fill light coming from the sun striking the sidewalk and the buildings behind me.

Fill Flash at 1:1 Ratio

I set my flashgun at full power to counteract the super bright backlighting from the sun. This gave me a 1:1 shadow to highlight ratio in the lighting.

related lighting products

The main light is sometimes referred to  as the key light.