In photography, an umbrella basically looks a lot like the type you use to keep the rain off of your head. However, these types of umbrellas are made to work like the reflectors used on floodlights.
Their main function is to provide a way of converting specular light into soft, diffused light.
A good umbrella will be able to wrap a subject in soft, bounce light with specular highlights.
The devices are made to be used with any type of light source as they can broaden, diminish, and soften the output of light from any source.
Umbrellas that have a white interior will be able to weaken and soften the light more than a shiny silver-lined model.
A white model that doesn’t have a black backing can also be utilized as a type of makeshift softbox. The size of the umbrella should be determined by the size of your subject and the strength of your lighting.
Some flash units are also often fitted with flash umbrellas, which are either made of a reflective material that bounces light back to the subject or diffusers that allow the light to diffuse through the material to reach the subject.
Both of them will create a larger effective light source which will be about the size of the umbrella.
Umbrellas can range in price from about $15 to several thousand.