I always like photography with back lighting, Silhouette is one of the popular output of it.It mainly depends upon framing sense and a proper exposure control.Different type of human expression, dramatic act, activity, shape, structure, modern art can be easily depicted with a little extra better angle of view. In fact silhouette can used to portray the natural beauty like sunrise or sunset also.The main feature of this kind of photography is foreground should be much darker than the background and the light coming out from the background area is used as the light source of the photography.We can easily control the amount of light in the photograph by maintaining the f-stop (exposure control) or by shutter speed.It is better not to increase the ISO because it allows more noise since the sensor gets more sensitive and as a result, picture having the darker area will get more noisy decreasing the overall quality of the picture.The edge separation between the subject and the background should be quite visible to make the picture more appealing.This technique is widely applied in studio photography while shooting the portrait with a proper shadow effect using a back lighting setup.
One more thing, try to fully cover the actual light source by the subject as much as possible to prevent the overexposed area.
Here are some example of 'Silhouette Photography'..