Softbox

Softness depends on how large the source appears from where the subject is standing. A bare bulb is a small source and throws hard, sharp-edged shadows; wrapping it in a box with a diffusion panel across the front spreads the same output over a much larger area, so the light wraps around a face and the shadow edge becomes a gradient. Moving the box closer makes it larger relative to the subject and therefore softer; pulling it back does the reverse. A grid fitted to the front narrows the spread and stops light spilling onto the background. Umbrellas do a similar job with far less control over where the light goes.