The Portrait Photographer’s Quick-ish Guide to Lighting Ratios | How To

Using artificial lighting is intimidating for many photographers. It’s easy
enough to know good natural light when you see it (though this too
takes practice), but artificial light requires a few extra skills to
create the look you want.

But oh, what a look you can make! To rapidly improve your artificial lighting skills, it helps to understand lighting ratios, or the relationship between how much power (ie., how much light) each light emits. In this tutorial we’ll start from scratch, looking first at what key and fill lights are, how they relate to each other, how to be precise
about this relationship, and finally why it makes a difference where your lights
are positioned. 

Then we’ll see how these concepts apply to
the ideas of “high key” and “low key” lighting, as well as adding other
lights into the mix.

Artificial Lighting Basics

The Qualities of Light

Not all light is equal! But what is “good” light? For photographic purposes, there are four qualities of light to consider:

• Intensity
• Colour
• Direction
• Texture

Control these four aspects, and you can light just about anything. This lesson from Scott Chanson’s course on artificial lighting is a great introduction:

Key Lights and Fill Lights

When talking about studio lighting, there are two main lights to think about: the key light and the fill light. 

• The key light is so-called because it’s the brightest light of the two, and is doing all the heavy lifting on the illumination. It’s the main light.
• The fill lights “fills-in” the shadows cast by the key light. 

When
the key light has illuminated one side of the subject, the other side of the subject is cast into shadows. A the fill
light adds light ,and stops the shaded side of the subject from
disappearing into blackness. So the fill light also helps to define the
shape of your subject and provide extra detail.

The key and fill
lights make up the classic two-light setup, but you can add other lights
too. These are things like rim lights—used to provide extra separation
of the subject from the background—and hair lights or other lights.
Additional lights and modifiers, of which there are many, can accentuate or change the look of a light, too.

• 

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  What Is Brightness? How to Understand Value in Photographic Lighting

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How to Calculate Lighting Ratios

Now that we’ve reminded ourselves what the key and fill lights are, how do they work together?

Basic Scenario: Same Lights, Same Distance, Different Power

Let’s
assume you’re using two identical lights, placed the same distance from
your subject with the same light modifiers. In this example, we can
find the lighting ratio by calculating the how much light each light
sends out compared to the other. Like so:

• If the
  key light is on 1/2 power, and your fill light is on 1/4 power, the key
  to fill ratio is 2:1: for every two rays of light key lights emits, the
  fill light emits one ray of light
• If the key is 1/4 power
  and the fill is 1/16 power, the ratio would be 4:1. The key light emits
  four rays of light for every one from the the fill

All Light Modifiers Change the Amount of Light

If
we’re using bare light bulbs it’s easy to calculate lighting ratios.
Common light modifiers like softboxes or umbrellas, however, make it
more challenging because in changing the light they all absorb a little
bit of it, and thereby change the amount of light that actually reaches
your scene.

So light modifiers alter the effective power
of your strobes: they spread the light around, softening and dimming it.
Just because the dial says 1/4 power, doesn’t mean you’re actually
getting that much light onto the subject. Ultimately, you just need to
know how much each modifier knocks off your power setting, and adjust
accordingly.

You Need to Measure the Light to Know the Ratio

When
it comes to artificial lighting, what really matters isn’t the power
ratio, or “incident” ratio, but the “reflected” ratio. This the
measurement of the amount of light that bounces off your subject and
back to your camera. Light is altered by all kinds of factors,
everything from skin tone, to ambient light, to how much dust there is
in the air. You need to use a light meter to find the reflected ratio for your lights as they are really working in your actual scene. 

• 

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  How to Use a Hand-Held Light Meter to Make Perfectly Exposed Photographs

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When we’re looking at the reflected ratio, what are we
measuring? In short, it’s the ratio of the amount of light reflected by
the highlights versus light reflected by the shadows. So regardless of
the exact power levels on your lights, if the light meter or your
histogram is saying the highlights are two stops brighter than the
shadows, you have a 4:1 lighting ratio.

Overlapping Lighting

If
the light from your key light and fill light overlap on the subject,
then you have an area of highlight that is brighter than either of them
alone. This is often called an incident ratio.

To account for
this overlapping light, you can either reposition lights so that it
changes the area that is “doubly lit”, or adjust the power down a
little, proportionally.

Distance

So far we’ve
kept our hypothetical lights at the same distance but, of course, that
distance plays a part in all of this. Light dissipates as it travels: it
spreads out in all directions. This means the further a light is from
the subject the less light falls on the subject. 

The inverse square law shows
us that a minor change in the distance of a light greatly impacts the
amount of light that hits the subject. It’s too complicated to get much
into here, but here are two handy rules of thumb: 

• Increase
  the distance between the light and subject by double and your subject
  will receive one quarter the light (from that light)
• Reduce
  the distance between the light and the subject by half and your subject
  will receive four times the light (from that light)

• 

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  Rules for Perfect Lighting: Understanding The Inverse-Square Law

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Lighting Ratios In Practice

In short: the power of
the lights is just a starting point. The light that actually reflects
off the subject and onto your film or sensor is what matters for the
exposure. Start by choosing the lighting ratios on your lights, and then
measure to account for reflectors, skin tone, and more. Then observe
your lighting and adjust the power, position, or modifiers to get the
look you want.

The terms high key and low key describe
two popular styles of lighting. They’re only two of many lighting
styles, but they are good ones for beginners because you can do a lot
with them and they each teach you a lot about how light works.
Photographers of all experience levels can apply and adapt these styles
to their own purposes, bend the rules, and play with them as visual
starting point.

High Key Lighting

High key is bright,
soft, low-contrast imaging, where the lighting ratio is around 1:1. This
virtually eliminates shadows and a lot of small detail; all that’s left
is strong details and outlines of forms. The eyes, bottom of the nose,
and lips can all stand out. It’s usually strongly illuminated from
behind, too, whether through backlighting or a bright solid white
backdrop.

The
term “high key” comes from early cinema and TV. The film and sensors
used couldn’t deal with strong contrast then, so the actors had three
lights on them to kill the shadows. We’ve come to associate this look
with cheerfulness, even as many TV shows try to move away from the
“cheap” look. Fortunately for us photographers, it’s not considered
cheap-looking in still images. 

Making a high key image is not
very hard. Even without arranging artificial lights, a combination of
sunlight and reflectors can create a high key look.

• 

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  The Complete Beginner’s Guide to Shooting High Key

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Low Key Lighting

Low key is the opposite,
stylistically: the lighting ratio is unbalanced, usually heavily,
producing a strongly affected image. A ratio between 4:1 and 8:1 will
usually achieve the low key feel. 

Low key lighting creates deep
shadows around all forms and structures of the subject. It’s a moody,
sometimes gritty look used for dramatic portraits.

While
we often now generally associate it with film noir, the effect
ultimately really comes from the Renaissance painting effect of
chiaroscuro (Italian, “light-dark”). Chiaroscuro could be hard or soft
lighting, but the intent was always to bring the three-dimensionality of
the subject’s form to life through directionality and shading.

So
while the effect has history in various art media, in stills it
sometimes comes across as cheap because of the simplicity of the setup
required to achieve it. When done well, however, low key creates a very
dramatic portrait.

• 

  Lighting

  The Complete Beginner’s Guide to Shooting Low Key

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What About Other Lights?

So what about those other
lights that aren’t the key and fill? Primarily what we’re talking about
here is the backlight or rim light, used to create a strong outline of
light around the subject to pull them off the background and into the
image. These lights aren’t considered a part of the lighting ratio we’ve
discussed so far, as they add supplementary light and don’t usually
change the light falling on the main focus of the image. 

However,
stray light and reflected light can change the highlight to shadow
ratio, so you do need to pay attention to how much light your extra
lights are contributing. Mostly you want them at least two stops under
your key light (that’s 1/4 the power), because the hardness and angle of
reflection mean that they can create flare in your photos, even at low
power.

Lighting Ratios and Shoot Management

On every paying photo shoot, time is money. More importantly, many people are anxious about being photographed, in a hurry, or both. A well-run shoott keeps everyone happy and looking good.

You
don’t have to be a technical expert to create well-lit photos. Many
skilled photographers never think about lighting ratios at all. Does
that mean you shouldn’t have a good grasp of lighting ratios? No! 

Just
like the inverse square law and other rules of lighting, the more you
know, the better and faster you can prepare. Here’s what will happen if
you get comfortable with lighting rations: 

• Your shoots will be more directed, with less trial and error, and far fewer mistakes
• You’ll start to notice little things about your lighting that you didn’t notice before
• You’ll start trying to figure out how other photographers did their lighting
• You’ll start to imagine new, creative ways to light

And
then, then the really cool things will happen: your shoots will start
to move smoothly and feel easy. You’ll you’ll be able to communicate
efficiently with your subjects, to tell them exactly where and how to
set the lights. You won’t waste anyone’s time.

When
you’re trying to create a specific lighting look, it helps to have
knowledge of how to arrange and power your lights. Using your light
meter, the camera’s histogram and reviewing your lighting results as you
go are an easy way to create exciting looks.

Keep on Learning

Lighting is a fascinating, fun thing to learn. Here are some more tutorials on lighting from Envato Tuts+: