|Not the strongest example of backlighting but it works.|
Although the image is backlit, it is important for the photographer to still pay attention to the light falling on the subject from in front. All too often, I see backlit images that die on the page because one cannot make out anything other than the strong rim light. In most cases, a person should be easily recognized in a backlit picture. Faces shouldn't just fall into the deep shadows and be lost, unless you are trying for a dramatic, artsy image.
Fiona has lovely red hair and the warm back lighting not only created nice highlights but made her wayward curls easy to see and to appreciate. The soft light falling on Fiona's face is as important to the picture as the backlighting. Having all the light sources working together makes this image work.
And how did I figure out my exposure? I let my Canon PowerShot S90 do the work. (Although I knew the exposure would be weighted for the face. The camera was set for centre weighted exposures.)