What is a Lighting Ratio? Photography Definition and Examples

This is a guide covering lighting ratio.

In this glossary definition you’ll learn about:

Throughout your journey in photography, there will be times when you stumble upon this term.

Generally, the lighting ratio is used in studio settings where you are given the opportunity to adjust key and fill lights.

Let’s dive in.

lighting ratio

What is a Lighting Ratio?

The lighting ratio definition is the comparison between the main source of light (key light) and the fill light.

With key light being the main source of where the shadows fall, the fill light will then “fill” in the shadows. When both of these light sources are used, a softer light will then be created on the subject.

A higher lighting ratio will make your image more contrasting. On the flip side, the lower your ratio is the lower contrast you will have. The ratio is based on the brightest part of your subject to the least bright parts.

Some photographers use (K+F): F for their lighting ratios, unless for contrast ratios over 4:1. For contrast ratios over 4:1, photographers often use K: F for its accuracy.

Light is measured in foot candles. Say the key light is 100 foot candles while the fill light is at 100 foot candles, the ratio will be 1: 1.

If the key light is at 200 foot candles and the fill light is 100 foot candles, the ratio will then become 2:1.

This ratio is also determined by the stops. Each time you increase the stop, the brightness will then double. On the other hand, each time you decrease the f stop by one, the brightness is half as bright as it originally was.

Changing the stops can be done through various methods such as; changing the exposure triangle, changing the intensity of the light sources, or manipulating the distance between your subject and the lighting

Let me explain the exposure triangle and how it affects your exposure. The exposure triangle is essential to the exposure of your images since both aperture and shutter speed physically affects your camera’s ability to absorb light. In short:

  • Aperture: This setting will affect your depth of field. If you use a large aperture the depth of field becomes shallower and more light can be absorbed by the camera. The reverse applies if you are using a smaller aperture.
  • Shutter Speed: Essentially, it’s the time your shutter can open-close-open. Faster shutter speed will allow you to “freeze’ moving objects, saving you from the usual blur when capturing a moving object. Since a fast shutter speed closes so fast, it doesn’t allow much light to enter. Slow shutter speed is more vulnerable to motion blur, but let’s in more light.
  • ISO: This setting simply brightens your photo. Most cameras nowadays can shoot using 3200 ISO before emitting visually unflattering noise. ISO helps you by providing flexibility in changing your aperture and shutter speed.

With all the important factors affecting exposure explained, let’s talk about common ratios.

purpose of key light

What are the Common Lighting Ratios?

Common lighting ratios will always differ depending on the situation you’re in and the client’s request. But, I assume that you’re referring to the lighting ratio for portraits inside a studio. Lighting ratios in a studio can vary depending on the agreement between the client or personal tastes.

Generally, professional photographers will aim for a realistic, flattering, and three-dimensional image.

Firstly they prioritize separating the subject from the respective background. Nowadays, it becomes too easy to introduce too much light onto your subject and erase all of the subject’s shadows.

The basic ratio is 1:1. This ratio provides an evenly lit subject from both sides, it doesn’t have any noticeable shadows and sometimes makes the image rather flat.

The subjects still look great, the light is still flattering, yet it feels incomplete. Generally, fashion and beauty photography will use this ratio to make their subject look flawless (no wrinkles, acne, pores, etc).

1 to 1 lighting ratio
Photo by Sound On

Then, there is the 2:1 ratio, with a one stop difference from the highlight to the shadow. The light is enough to add a dimension to the image. Yet the light is so soft, which creates the perfect ambiance for child photography. It makes the image feel a bit innocent and pure.

newborn photography 2 to 1 lighting ratio
Photo by Adele Morris

With a two stop difference between the lights and shadows, there’s the 4:1 ratio. This is the most commonly used light ratio for portraits. It serves as an all-around light ratio that can be used in most types of photos. A decent amount of shadow makes the image livelier than the 1:1 ratio.

portrait 4 to 1 lighting ratio
Photo by Darya Skuratovich

Lastly, is the 8:1 ratio with a 4 stop difference? It produces an almost perfect amount of light and shadow on your subject. With this ratio, your image becomes more dramatic and much more flattering for your subject.

portrait 8 to 1 lighting ratio
Photo by Brent Ninaber

That is all! The four ratios mentioned above are the most commonly used in portrait photography. Of course, everyone has their own preferences and style when it comes to photography. Feel free to explore and experiment with the various light ratios and equipment to see which works best.

There are tons of lighting ratio charts available online to download and print, which can help you decide the ratio you want for a certain image. The more you get used to your lighting ratio, the faster you’ll recognize the most appropriate ratio.

How Key Light Affects Lighting Ratio?

By definition, the key light is your brightest light source. As the main source of light, it controls the ratio and the amount of light/shadow intensity.

The key light is oftentimes used in the three-point lighting method, accompanied by the fill light and backlight/hair light. Photographers are free to place their main lights wherever they please in the studio.

The main purpose of your key light is to illuminate the subject, provide highlights towards the form, and lastly the dimension of the subject.

An image can still be taken without a key light in it. The result will make a silhouette effect that looks pretty cool, edgy and reminds me of James Bond.

High-key lighting will reduce the scene’s lighting ratio. This translates into less contrast between the bright and dark areas. Less contrast between both of the elements creates an upbeat mood, which is often followed up by a positive message.

You’ll often witness this type of lighting in video interviews, educational videos, training videos, and many more.

To produce this message loud and clear, your content and lighting must work hand in hand. If you deliver a negative message using high-key lighting, your audience might capture a confusing message.

But this is by no means a restriction on your creativity and serves as a rule of thumb. As a fellow photographer, I encourage you to experiment and have fun with it.

There is also low-key lighting that gives you the least amount of midtones and whites. Photographers have been using this technique to create a more dramatic and mysterious mood for the image.

With the lighting technique that shows a moody dark tone with a hint of seriousness and mystery, it naturally looks better in black and white.

Film noir and crime dramas just love using low-key lighting, their themes thrive in the high contrast lighting.

You will barely see low-key lighting in advertisements or promotional material due to its ambiance. Even if you see one, it will most likely tip to the more emotional and gloomy side.

key light brightness

How Fill Light Affects Lighting Ratio?

Fill lighting serves a more complementary role if compared to the key light and backlight. Fill light basically fills in the shadows that are created by the key light. The strength of the fill light will never be over the key light, at most, it’ll be on par with the key light.

As a light that is mainly used to fill the shadows, photographers don’t really use too much fill. To maintain a sense of drama, they use a lot of key light and minimum fill light. For scenes that need to look more upbeat and positive, they’ll use a fill light with the same strength as the key light.

studio light meter

How Do You Determine a Lighting Ratio?

Determining your light ratio is somewhat difficult yet easy at the same time. Sometimes, you can just use the same lighting ratio over and over for multiple photo shoots since they are quite “neutral.”

Photographers commonly use the 2:1 ratio when photographing babies and children. The 8:1 ratio is more appropriate for artistic portraits that want to show personality and seriousness.

The best option is to adapt based on your theme, subject, and client’s expectations. The 1:1 is better at hiding your subject’s imperfections. Each ratio has their most optimal uses, but there are photographers that experiment with the limits of each lighting ratio.

To measure the lighting ratio, you’ll need a light meter. There are many affordable and useful light meters on the market, but the most popular one is the Sekonic Light Meter 308s.

To use this light meter, place the dome on the brightest area of your subject and face it to the light source. This will then show you how bright your key light is. After that, you’d do the same procedure on the less bright area on your subject. The f-stop will show you how bright the fill is.

The indicator will show you in increments of stops and voila. Read our article about the light meter for a more detailed explanation.

What Lighting Ratio Would Virtually Eliminate Shadows?

If you’re talking about a fully illuminated face from each side, then it’s the 1:1 ratio. It looks good on certain images, it makes them look more flattering and beautiful. But shadows actually play a larger role and they’re not just a nuisance.

Shadows appear when an object blocks the light source, making the object’s shape projected onto the shadow.

Good use of shadows will help direct the viewer’s attention towards a specific location. It reveals features that are maybe better off unseen. They add drama, emotion, and mystery to the photo.

Final Remarks

So, what is the lighting ratio? It’s the ratio of key light to fill light. There are the 1:1 (with virtually no shadows), 2:1, 4:1, and 8:1 ratio (with the most shadows) are commonly used.

But each ratio has its own uses and ambiance depending on the key light and fill light. The key light is your main (brightest) light, while the fill light “fills” in the shadows.

Knowing when to use certain ratios may be hard at first, so consider using a lighting ratio at first. The more you practice and use lighting ratios in your photo shoots, the faster you’ll get accustomed to it. Have fun and good luck!

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