Two Light Setups
It is important to remember that all the concepts we looked at in a single light setup still applies to each light you add into you overall setup. Types of modifiers, distances, power settings relate to all of the lights in your setup and contribute to your final image.
For the ultimate control of exposure you should consider metering the exposure of each light in turn. This way, for example, you could say you want a fill light to be 2 or 3 stops lower than your key light. You would meter your key light to say, f8, turn it off, and then meter your fill light to get f4 or f2.8. In this day and age though it is too easy to look at the image on the back of the camera to see the overall effect but this can be unreliable depending on how well you LCD is calibrated. Likewise you might shoot tethered giving slightly more reliable results especially if you have calibrated your monitor.
With that in mind let's look at adding a second light into the mix.
Adding a background light
Adding a background light can be one of the first uses you have for a second light. We usually add a background light to give some definition between our model and the background itself - especially if the background is dark and our model has dark hair or clothing.
A simple reflector dish with a grid creates a nice pool of light behind Pixie Elle's head giving definition to her hair which would otherwise probably blend into the background. Typically a reflector dish is used for this type of setup but remember it's your choice and you might want to use a different type of modifier like an optical gobo to create a pattern. You could also add coloured gels to the reflector to change the colour of the light pool. Also, experiment with how far away from the background you position the light, the closer in it is the tighter and more intense the pool of light.
Add a hair light
Another way we can add definition to our model is by adding a hair light. Again this works particularly well when shooting against a dark background.
An important thing to remember about hair light is that the exposure required will change depending upon the colour of the models hair. Dark hair will absorb more light so the light power needs to be increased. Lighter hair reflects light so a lower power setting should be used to avoid blowing out the detail.
Add a fill light
A fill light can be added to lift the shadows much like when a reflector was used on a single light setup. Sometimes this may give you a bit more control than trying to use a reflector.
Adding the fill light lifts the shadows on the opposite side of the key light and can also provide a bit more definition around the hair if you are shooting dark hair against a dark background. The type of modifier you use though will determine what shadows are filled in. Here we have used a rectangular soft box which suits the three quarter length shot nicely but if we were shooting full length we might opt for something like a strip soft box.
Clamshell lighting
Clamshell lighting is a fairly specific style of beauty lighting reducing overall shadow on the model's face and reducing any blemishes.
With this style of lighting a key light is placed directly above and slightly forward of the model, pointing towards the face. A second fill light is placed below the model and aimed upwards. Typically the lower light should be between a 1/3 and 1/4 of the power of the key light to prevent shadows being cast upwards - generally not a good look. You can replicate this setup with a single light if required by using a reflector instead of the second fill light. You can buy snazzy beauty reflector kits (tri-fold reflectors) but to be honest a piece of white card would do the trick.
I have used an octagonal soft box here but often a beauty dish will be used as the key light. The harder light created by a beauty dish will give a more contrasty image and sculpt the face more.