The term used to describe the relationship between light and dark in an image is described as the “light ratio”. What this defines is the difference in exposure between the highlighted area of a subject and the darkest shadowy area.

The lighting ratio is an indication of how much shadow detail you will have on the final nude body or the model’s face.

Important: a ratio is always based upon different lighting power, rather than EVs or f/stops.
Whenever I talk about or show f-stops in this article, it’s simply to illustrate the different light areas in a less complex way so the topic will be easier to understand. And as photographers, we are all rather thinking in f-stops. So this concept is much easier to grasp than me talking about light-power-percentage.

Glowy Glam Uses 3:1

Light Ratios - Plasticity & Dimension in Nude Photography

A desirable ratio for glam photography is 3:1. This ratio guarantees both defined highlights and shadows and is useful in a wide variety of situations.

If you go black & white “artsy-style”, you can play around and impose with high ratios which lead to stronger contrasts in the final results.

Working With Key & Fill Light

In order to understand and balance the relationship between lights, it is helpful that you work with your trusty light meter.
The meter will simply show you the relevant f-stop figures when metering the key light and the fill-in(s). By understanding the readings of your meter, you can predict the outcome of the shot before you even start shooting.

The key light is always the base. It’s the “1” in ratio scale. The fill light’s job is to influence the shadow areas.

  • No fill = shadows stay the way they are created by the key light
  • Too much fill light = you create a new key light
  • 0% to 90% fill light power: determines the style you are going for

Light Ratio Simulation

Light Ratios - 3D Simulation Lighting Setup
The light ratio simulation here is based on a key light and a fill light. I am increasing/decreasing the fill-in related to f-stops (aperture). I am not manipulating the camera’s aperture at all but need the f-stops to explain the ratio.

Light Ratios - F-Stops & Aperture Formula

The f-stop values on your lens represent a doubling or splitting in half of the light that reaches the sensor.

  • For example, f8 would allow in twice the light that f5.6 would.
  • So if you have a main light that you have metered at f8 and then you turn off this light and meter your second (fill) light and get 5.6, you have a 2:1 ratio. The reason for this is that the main light is producing twice as much light as the fill light.
  • If you have a 2 stop difference in your readings, this means 4 times as much light from your main light so a 4:1 ratio, 2×2=4.
    If there is a 3 stop difference you have a lighting ratio of 8:1, 2x2x2=8.

You got it…

Real World Light Ratio Test

Light Ratios - Behind the Scenes - Studio Photography Ligting Setup
For providing a better visual understanding and proof I shot that test in a studio under real-world conditions.

Note that key- and fill-in light positions are just flipped but the ratio test setting stays the same.

The ratios are not affected in any way, regardless of where you basically position your lights.
Remember, it’s the luminosity relation between the different sources.

Ratios are always measured between the brightest and the darkest part on your main subject.

Light Ratios - Model Melisa Mendini - Nude Photo - Lighting Results

ESSENTIALS. Studio Lighting for Nude Photography feat. Jenni Czech & Melisa Mendini

ESSENTIALS. Studio Lighting for Nude Photography

Lighting Blueprint. Theory, showcases and exercises. Extensive theory part to strengthen your practical work. 19 all-inclusive case studies/lighting setups for 1, 2, 3 & 4 lights. Featuring Jenni Czech & Melisa Mendini. Sexy Women Photography at its best!