Lightbanks or soft boxes emulate the soft, directional lighting produced by window light so they’re usually rectangular but they can be any shape. Striplights that emulate stage footlights produce dramatic portrait lighting. Lightbanks can also be octagonal that produce a direct yet wraparound light source with even light spread. I shot a test using three different shaped Flashpoint soft boxes…
For the unretouched photograph at left a single 36 x 48-inch Flashpoint PZ Softbox was placed at camera right. Exposure with a Canon EOS 5D and EF 28-135mm f/3.5-5.6 IS USM lens was 1/125 sec at f/10 and ISO 100. In each of the following examples, the background becomes darker or lighter depending on the shape of the light from the softbox
Here I used a 12 x 36-inch Flashpoint PZ Softbox ($84.95) aka striplight. The light is at camera right and the exposure with Canon EOS 5D and EF 28-135mm f/3.5-5.6 IS USM lens was 1/125 sec at f/8 and ISO 100.
If any lightbank could be called the Goldilocks light source it would be the 36 x 36-inch PZ Octabox. It provides a wraparound soft light and seems to be the perfect light source. Exposure with Canon EOS 5D and EF 28-135mm f/3.5-5.6 IS USM lens was 1/125 sec at f/10 and ISO 100.