I will just share the lighting diagram and the gear used to achieve this shot.
1 X DSLR camera + 50mm f1.8 lens
2 X off camera flashes.
1 X umbrella softbox with grid
1 X light meter.
To achieve a shot like this would be particularly difficult without some form of intentional external light source. I used two flashes, one as a main light and the other to add something different to the background. I just took a reading using my light meter from the main light to determine the exposure on the model. At first the flash was too weak because I was using a softbox to diffuse the light and to get a good quality of light on the model. I had to adjust the flash output to 1/2 power to achieve an exposure of f4 (at ISO400).
For those of you who dont know, different diffusers give you a different quality of light. Umbrellas give you soft, non-directional lighting. That means it throws the light everywhere although mostly in the direction opposite of your reflective surface. Softboxes also give you a soft but directional quality of light. This means you have some control regarding where your light is going. And adding a grid just gives you even more control. I adjusted the purple-gelled light a stop and two thirds bellow my main light so that it's not too bright.
I took the shot and it came out quite good first time round. All I had to adjust was a bit of contrast and clarity. Remember to strive to get a shot right in camera to reduce the time you spend editing and retouching!! I hope this helps someone out there trying to understand lighting and exposure! If anyone else would like to comment or share any info, please feel free to post!
Oh ya, and you can get most of these little gadgets at:
ORMS (Capetown, South Africa)
Adorama (NYC, United States)
Out Door Photo (Garsfontein, Pretoria, South Africa)
Kameraz (Rosebank, South Africa)