Establishments producing daguerreotype portraits generally had a daylight studio built on the roof, much like a greenhouse. Whereas later in the history of photography artificial electric lighting was done in a dark room, building up the light with hard spotlights and softer floodlights, the daylight studio was equipped with screens and blinds to control the light, to reduce it and make it unidirectional, or diffuse it to soften harsh direct lighting. Blue filtration was sometimes used to make it easier for the sitter to tolerate the strong light, as a daguerreotype plate was almost exclusively sensitive to light at the blue end of the spectrum and filtering out everything else did not significantly increase the exposure time.